LIAM2 Microsimulation made EASIER en-us Tue, 24 Nov 2015 00:00:00 +0100 <![CDATA[Version 0.11 released]]>

Version 0.11 released

Highlights of this release are support for the “sidewalk” alignment method, support for default values for fields and some basic help in the interactive console.

Download this release from the download section.

New features

  • added support for the “sidewalk” method in align_abs() in addition to the existing (and default) “bysorting” method. Thanks to Alexis Eidelman and Mahdi Ben Jelloul (pull request 189).
  • added support for defining a default value for fields. This default value will be assigned to the corresponding fields in new() and if the fields are not present in the initial data (see the fields declaration section for details). Thanks to Alexis Eidelman and Mahdi Ben Jelloul (pull request 190).
  • added “functions” command to the interactive console. It displays the list of available functions.
  • added “help [function]” console command. It displays the signature of the function (ie the list of possible arguments and their default value if any). For random generator functions it also displays a detailed description (from numpy).
  • added a ‘limit’ argument to dump() to limit the number of rows of the output.

Miscellaneous improvements

  • improved the logging message for align with take or leave filters: the take and leave filters are combined with the “normal” filter before computing the take and leave numbers displayed. It does not change the results in any way, only the numbers logged to the console.
  • made the demonstration models use 3d alignment files in some cases instead of separate alignment files for men and women.
  • better error message when a user-defined function is called with the wrong number of arguments.
  • better error message on failed assertEqual if shapes are different.
  • added check for duplicate ids when loading datasets.

Miscellaneous improvements for developers

  • implemented Simulation.from_str to create a simulation object from a string (using Python).


  • fixed various problems with the demonstration models.
  • fixed grouping by a constant.
Tue, 24 Nov 2015 00:00:00 +0100 <![CDATA[Version 0.10.5 released]]>

Version 0.10.5 released

This is a bug fix only release.

Download this release from the download section.


  • fixed using one2many in combination with lags of more than 1 period (or any past period in the interactive console).
Fri, 13 Nov 2015 00:00:00 +0100 <![CDATA[Version 0.10.4 released]]>

Version 0.10.4 released

This is a bug fix only release.

Download this release from the download section.


  • fixed a few issues with the demonstration models.
  • fixed 0.10.3 change log to mention Christophe Benz.
Thu, 12 Nov 2015 00:00:00 +0100 <![CDATA[Version 0.10.3 released]]>

Version 0.10.3 released

Highlights of this release are improved demonstration models, better Linux support, better automated tests and the usual assortment of fixes and miscellaneous improvements.

Download this release from the download section.

New features

  • added seed() function to (re)set the pseudo-random generator seed mid-simulation.

Miscellaneous improvements

  • updated demo models:
    • improved the dataset (which is now generated by a LIAM2 model: generate.yml).
    • reorganise the models to group presented features more thematically.
    • added more comments.
    • added example of progressive .csv files via mode=’a’.
  • added installation instructions and generally improve the out of the box experience on Linux. Thanks to Mahdi Ben Jelloul (pull request 181).
  • enabled running the unit tests automatically on each change to the GitHub repository by using Travis-CI (which runs tests on build servers). Thanks to Mahdi Ben Jelloul and Christophe Benz (pull request 182).
  • added an explicit error message when using “empty” processes (ie a “-” without any other text).
  • moved website to its own repository (
  • renamed “src” folder to “liam2” to follow standard practices. Thanks to Mahdi Ben Jelloul (pull request 181).
  • improved error message of assertEqual if the array shapes are different.
  • added explicit test for logit_score.


  • the list of available periods in the console is sorted.
  • fixed time travel in the console at the end of a simulation.
  • fixed writing technical error (traceback) in error.log.
  • fixed the explore command on .h5 files.
Thu, 05 Nov 2015 00:00:00 +0100 <![CDATA[Version 0.10.2 released]]>

Version 0.10.2 released

This release fixes a few more bugs I remembered about just after I finished the 0.10.1 release.

Download this release from the download section.


  • fixed the fields command in the interactive console (closes issue 176).
  • if there is only one entity defined, start the interactive console in that entity, even if default_entity is not set (closes issue 175).
Wed, 24 Jun 2015 00:00:00 +0200 <![CDATA[Version 0.10.1 released]]>

Version 0.10.1 released

This is a minor mostly bug fix release.

Download this release from the download section.

New features

  • allowed to override all simulation options except “init” and “processes” using the command-line. Run “main run -h” for details (closes issue 173).


  • fixed the error message when using an unknown variable to be more explicit like it was in versions before 0.9 (closes issue 167).
  • the output of the demonstration models is no longer included in the bundles (closes issue 169).
  • made simulations which terminate in an error exit with the correct error code even without –debug (closes issue 174).
Mon, 22 Jun 2015 00:00:00 +0200 <![CDATA[Presentation at the IMA conference in Luxembourg]]>

Presentation at the IMA conference in Luxembourg

I will be giving a presentation titled “LIAM2 - overview and recently added features” at the Fifth World Congress of the International Microsimulation Association, 2-4 September 2015, Luxembourg.


This presentation will be divided into two parts. First a quick overview of what is LIAM2, then a description of all the new features since the LIAM2 course at the IMA conference in 2013 and more briefly those since our initial presentation in 2011. Each of those features will be briefly explained with examples of how they were used in real models.


LIAM2 is a free, open source, user-friendly modelling and simulation framework. It is made as generic as possible so that it can be used to develop almost any type of discrete-time dynamic microsimulation model with cross-sectional dynamic ageing (i.e. all individuals are simulated at the same time for one period, then for the next period, etc.). LIAM2 is clearly aiming to free “modellers” from having to develop or care about having state-of-the-art methods for data-handling or expression evaluation and yet be able to handle relatively large datasets at a reasonable speed. For example, a model like MIDAS in Belgium simulated over 60 years with 2.2 million individuals initially could be developed in a user-friendly environment and is run in less than 4 hours. To date, LIAM2 has been adopted by modellers in at least 7 countries.

New features since 2011

  • model imports and model variants
  • many new functions including:
    • charting functions
    • aggregate functions: gini, percentile, ...
    • new alignment options (using absolute values or on a linked entity using Chenard’s algorithm)
    • debugging functions (assertions, ...)
  • data viewer (HDF5 viewer)
  • syntax changes
  • officially open source and hosted on GitHub

New features since 2013

  • user defined functions
  • while loops
  • improved handling of external data
  • new matching algorithms
  • more random number generators
Fri, 19 Jun 2015 00:00:00 +0200 <![CDATA[Autumn school on modelling using LIAM2 at LISER (Luxembourg)]]>

Autumn school on modelling using LIAM2 at LISER (Luxembourg)

In the context of the InGRID network, the Luxembourg Institute of Socio-Economic Research (LISER, formerly CEPS/INSTEAD) is organizing a workshop on “Elaborating a discrete-time dynamic microsimulation model with LIAM2, an open source development tool”.

The workshop is free of charge and will take place from 16 to 18 November 2015 in Luxembourg. Travel costs and accommodation are reimbursed up to certain amounts. See for all the details.

Fri, 19 Jun 2015 00:00:00 +0200 <![CDATA[Version 0.10 released]]>

Version 0.10 released

Highlights of this release are the implementation of while loops and calling user-defined functions, potentially with arguments. Please also see the complete release notes below for a potential migration issue concerning code defined outside of functions/procedures.

Download this release from the download section.

New features

  • implemented support for calling user-defined functions (previously called procedures) from within user code, optionally passing arguments to them and retrieving their return value. As a consequence of this, every mention of “procedures” in the documentation has been replaced by “functions”, including the name of the “procedures” logging level which is now deprecated. Closes issue 152.
  • implemented while loops (closes issue 151).
  • added support for not storing some fields in the output file (closes issue 58).
  • added support for using the “inf” (infinite) constant.

Miscellaneous improvements

  • improved our error handling code to display the (part of the) line where the error occurred in more cases and to not strip the traceback (error.log) of some important information in the cases where the line was already displayed.

  • configured the bundle editor (Notepad++) to display some warning and error lines in red in the console log. Additionally, when the error message contains a filename and/or a line number (this is currently too rare unfortunately), it is now click-able (to jump directly at the file/line).

  • defining a process outside of a function has been deprecated because it is ambiguous. For example, this code will now trigger a warning and will be an error in a future version:

                agegroup: int
                agegroup: 10 * trunc(age / 10)
            - person: [agegroup]

    It should be replaced by (or possibly moved into another existing function):

                agegroup: int
                    - agegroup: 10 * trunc(age / 10)
            - person: [compute_agegroup]

    If this construct was used to have a temporary field (ie the field was not declared in the fields section) accessible from several functions, like

                tempfield: 0
                    tempfield: count()
                    otherfield: tempfield + 1

    One should now declare that field with output: False instead.

                tempfield: {type: int, initialdata: False, output: False}
                    tempfield: count()
                    otherfield: tempfield + 1

    This closes issue 124.

  • made bcolz optional (which is only useful for interpolating the dataset during import). Thanks to Mahdi Ben Jelloul (pull request 161).

  • allow simulations with no processes section (but an init section).

  • reworked a few sections of the documentation.

  • trying to set a value to an unknown variable in new/clone produces a warning instead of being silently ignored (or even crashing with –debug)


  • fixed end-of-simulation stats when simulating 0 periods (closes issue 158).
  • allow overriding (detected) field types of period and id fields in import (closes issue 154).
  • fixed autodump (broken in 0.9). Note that it is currently incompatible with while loops and recursive (user-defined) functions.
Mon, 15 Jun 2015 00:00:00 +0200 <![CDATA[Version released]]>

Version released

This is a remake of the 0.9.1 release with a correct version number and other packaging fixes.

Download this release from the download section.


  • fixed version number (release 0.9.1 reports itself as 0.9).
  • fixed various small problems with the release script.
  • made the 32b version use the exact same versions of third-party packages as the 64b version.
Tue, 14 Apr 2015 00:00:00 +0200 <![CDATA[Version 0.9.1 released]]>

Version 0.9.1 released

This is a bugfix only release.

Download it from the download section.


  • Alignment under and overflows are displayed again, even when debug is not set (closes issue 155).
  • Always load all declared entities even if there is no process executed for them (but produce a warning in that case). This used to cause a problem if an entity had no process but was used through links (closes issue 89).
  • Fixed dump when the filter is False (a scalar), for example in dump(filter=period == 2100) (closes issue 142).
  • Fixed the declared return type of many random distributions, which caused a problem if they were used with a filter or within an if() expression. This change also fixed cont_regr when both mult and filter arguments are used (closes issue 153).
Tue, 31 Mar 2015 00:00:00 +0200 <![CDATA[Version 0.9 released]]>

Version 0.9 released

Highlights of this release are many new random number generators, performance improvements, new matching algorithms, nicer internal code and many other smaller fixes and improvements.

Download this release from the download section.

New features

  • added support for most of the random number generators provided by Numpy which were not already supported by LIAM2: beta, chisquare, dirichlet, exponential, f, gamma, geometric, hypergeometric, laplace, lognormal, multivariate_normal, noncentral_chisquare, noncentral_f, pareto, power, rayleigh, standard_cauchy, standard_exponential, standard_gamma, standard_normal, standard_t, triangular, vonmises, wald, weibull, zipf, binomial, logseries, negative_binomial, poisson and multinomial (see the random functions section for details). Closes issue 137.

  • added the rank_matching() function as an alternative method to match two sets of individuals. Based on pull request 136 from Alexis Eidelman.

  • added an optional “algo” argument to the matching() function, which can be set to either “onebyone” or “byvalue”.

    • “onebyone” is the current default and should give the same result as previous versions.
    • “byvalue” groups individuals by their value for all the variables involved in both the score and orderby expressions, and match groups together. Depending on whether all individuals have different combination of values or not, this can be much faster than matching each individual in turn. It is highly encouraged to use this option as it is much faster in most cases and it scales better (O (N1g*N2g) instead of O(N1*N2) where N1g and N2g are the number of combination of values in each set and N1 and N2 are the number of individuals in each set). However, the results are NOT exactly the same than in previous versions, even though they are both correct. This means that simulation results will be harder to compare against simulation results obtained using previous versions. This will be the new default value for version 0.10. Please also note that this new option is only available if the C extensions are installed. In our test models on actual data, this version ran from 50% faster to 3x faster.

    This code is based on the optimized_matching work from pull request 144 by Alexis Eidelman.

  • added the possibility to automatically generate an order in matching() by using the special value ‘EDtM’ for its orderby argument. Based on pull request 136 from Alexis Eidelman.

  • added an optional ‘pool_size’ argument to matching(). If used, the best match for an individual is looked for in a random subset of size pool_size. Based on pull request 136 from Alexis Eidelman.

Miscellaneous improvements

  • updated bundled dependencies to their latest version. The numpy upgrade to version 1.9 brings some performance improvements in various areas (our test simulation runs approximately 15% faster overall).
  • large internal refactoring
    • it is now easier to define new functions (there is much less code to write).
    • all arguments to all functions can now be expressions. Closes issue 5.
    • cleaner variable scopes. Eliminates a whole class of potential problems when using two fields with the same name but a different entity (via a link) in the same expression. Closes issue 41.
  • cache some internal structure so that it is not recomputed over and over, which improves overall performance by a few percents in some cases, especially when computing many “small” expressions as is often the case in one-by-one matching() (which improved in our tests by 10-20%).
  • remove() can now be called without filter argument (it removes all individuals)
  • better and more consistent error messages when calling functions with incorrect arguments (too few, too many, ...)
  • use input/path as the base directory for loading .csv globals (those using an explicit “path”) instead of using the directory of the HDF input file.
  • nicer string representation of some expressions (this only affects qshow and groupby).
  • the –versions command-line argument now also shows versions for optional dependencies (if present).
  • improved many tests, especially the ones for matching().


  • fixed the “view” command (to launch ViTables – via F9 for example) in the 64 bit bundle. This was a regression in 0.8.2. Closes issue 147.

  • fixed computing most expressions involving arrays with more than one dimension. It only worked if all the arrays involved were based on the same “source” array (which was the case in our tests).

  • assertEqual fails gracefully when comparing two arrays with different shapes.

  • fixed global fields colliding with fields with the same name from other (global) tables.

  • fixed expressions like:

    if(filter_expr, align(..., array[scalar], ...), False)

    and made all if(expr, GLOBAL[scalar_value], ...) expressions faster in the process.

  • fixed a rare problem with some expressions using scalars returned by aggregate functions.

Tue, 03 Feb 2015 00:00:00 +0100 <![CDATA[Version 0.8.2 released]]>

Version 0.8.2 released

New features

  • allow loading globals from csv files directly, instead of having them in the input HDF file. One can mix both approaches (have some globals in the “input” HDF file while other globals in .csv files). This makes it more practical in case you have a relatively stable input dataset for entities, but need to change the globals often, or have several variants with different globals. See the globals section for details. This closes issue 30.
  • added a new simulation option category: “logging”. This is the new home for the existing “timings” option, and for a new “level” option, which allows to sets the verbosity of logging to one of periods, procedures (this is the default) or processes (which corresponds to the behavior in earlier versions).

Miscellaneous improvements

  • decreased memory usage for models with many periods. It used to keep the index of individuals of past periods forever in memory, which had approximately the same effect than adding one column for each period. Since it is only useful when going back in time more than one period, it now flushes it to disk for periods < period - 1. This change has two consequences: it will decrease memory use for models with many periods but will slow down models going back in time more than one period. This closes issue 130.
  • the “top times” at the end of the simulation now also include the % of total.
  • after each period, a very rough estimate of the remaining time for the simulation is displayed (closes issue 127 in combination with the logging/level option).
  • updated all dependencies provided in the bundle.
  • improved the release script.


  • Using links or other “non-simple” variables in the score expression of the matching() function was a lot slower and memory-hungry than necessary because some “system temporary variables” kept accumulating. It is still a lot slower than it should though, see issue 128.
Thu, 02 Oct 2014 00:00:00 +0200 <![CDATA[Version 0.8.1 released]]>

Version 0.8.1 released

New features

  • added the gumbel() function to draw random numbers from the Gumbel distribution (also known as the Smallest Extreme Value (SEV) distribution). Thanks to Gijs Dekkers for the patch.


  • fixed a performance regression in 0.8 when using very large negative numbers as indices for a global (eg MINR[bad_index] where bad_indix contains several -2147483648 values). Closes issue 121.
  • fixed the (debug) interactive console to not produce a useless warning if a global temporary was run before entering the console (regression in 0.8). Closes issue 120.
  • added missing documentation for assertFalse and assertNanEqual.
Wed, 19 Mar 2014 00:00:00 +0100 <![CDATA[Version 0.8 released]]>

Version 0.8 released

New features

  • added a few functions to create charts (courtesy of matplotlib): bar, plot, pie, stackplot, boxplot and scatter. As with all other functions in liam2, they are available both during a simulation and in the interactive console. The charts can either be visualized directly or saved to a file. See the charts section for details.
  • added a “view” command line option to LIAM2 to open ViTables (an hdf5 viewer) as well as a corresponding menu entry and keyboard shortcut (F9) in Notepad++. It is meant to be used when editing a model file, and it will open both the input dataset and the result file (if any).
  • document boolean aggregate functions: all() and any() which were added in 0.7 but were not yet documented.
  • added assertFalse assert function.

Miscellaneous improvements

  • improved the first few demonstration models quite a bit. A recommended read for all users.
  • added precisions in the documentation of align() based on Alexis Eidelman suggestions.
  • made a few more error messages a bit more useful by displaying the line where the error occurred.
  • sped up global[array_expr].
  • give a hint to use assertNanEqual when it would make a failing assertEqual pass.
  • implemented global[slice_expr] (eg. MINR[period: period+2]). When the slice bounds are arrays (different for each individual) and the slice length is not constant (not the same for all individals), it returns a special array with an extremely limited set of supported operations: only aggregates on axis=1 are implemented.
  • include the documentation only in HTML Help format (.chm) in the bundle. .pdf and “normal” html are still available as separate downloads on the website.
  • removed the predictor keyword support (it now raises an exception instead of a warning).
  • adapted the release script since our move to git and converted it to Python.


  • fixed the “syntax upgrade” script by removing a special case for grpmin and grpmax as it was in fact not needed and caused problems when the expression being aggregated contained parentheses.
Wed, 05 Feb 2014 00:00:00 +0100 <![CDATA[LIAM2 is on GitHub]]>

LIAM2 is on GitHub

The source code for LIAM2 is now hosted on GitHub:

This offers many advantages over what we did previously (create a snapshot of the code each time a new version is released):

  • one can follow the development as it happens (see what changed at any time, browse the source code at any revision, ...)
  • much easier integration of external contributions
  • more visibility for liam2
  • and much more...


Tue, 17 Dec 2013 00:00:00 +0100 <![CDATA[Version 0.7 released]]>

Version 0.7 released

New features

  • implemented imports so that simulation files can be split and reused. This can be used to simply split a large model file into smaller files, or (more interestingly) to create simulation variants without having to duplicate the common parts. This feature was inspired by some code from Alexis Eidelman. For details see the Importing other models section.
  • added new logit and logistic functions. They were previously used internally but not available to modellers.
  • added two new debugging features: autodump and autodiff. autodump will dump all (non-scalar) variables (including temporaries) at the end of each procedure in a separate hdf5 file. It can be used stand-alone for debugging, or in combination with autodiff. Autodiff will gather all variables at the end of each procedure and compare them with the values stored previously by autodump in another run of the model (or a variant of it). This can be used to precisely compare two versions/variants of a model and see exactly where they start to differ.
  • added new assert functions:
    • assertIsClose to check that two results are “almost” equal tolerating small value differences (for example due to rounding differences).
    • assertEquiv to check that two results are equal tolerating differences in shape (though they must be compatible).
    • assertNanEqual to check that two arrays are equal even in the presence of nans (because normally nan != nan).
  • added a new “timings” option to hide timings from the simulation log, so that two simulation logs are more easily comparable (for example with “diff” tools like WinMerge).
  • added a menu entry in notepad++ to run a simulation in “debug mode”.

Miscellaneous improvements

  • improved the performance and memory usage by changing the internal memory layout. Most operations are now faster. new(), remove(), “merging data” (for retrospective simulations) and writing data at the end of each period are now slower. In our model, this translates to a peak memory usage 20% smaller and a 35% overall speed increase. However, if your model has a low processes/variables ratio, it may very well be slower overall with this version. If it is your case, please contact us.

  • changed the syntax for all aggregate functions: grpxxx(...) should now be xxx(...). For example, grpsum(age) should now be: sum(age). The old syntax is still valid but it is deprecated (it will be removed in a later version). A special note for grpmin() and grpmax() which becomes min() and max() respectively even though those functions already existed. The meaning is deduced from the number of “non-keyword” arguments:

    min(expr1, expr2)

    minimum between expr1 and expr2 (for each individual)


    (aggregate) minimum value of “expr” over all individuals

    min(expr1, filter=expr2)

    (aggregate) minimum value of “expr” over individuals satisfying the filter

    A tool to automatically upgrade models to the new syntax is provided. In notepad++, you should use the LIAM2: upgrade model command in the Macro menu.

    You can also run it via the command line:

    main upgrade model.yml [output.yml]

    see main upgrade –help for details.

  • changed the syntax for all one2many link functions: xxxlink(link_name, ...) should now be For example, countlink(persons) should now be: persons.count(). The old syntax is still valid but it is deprecated (it will be removed in a later version). As for aggregate functions, one can upgrade its models automatically with the “upgrade” command.

  • the “period” argument of value_for_period can now be a scalar expression (it must have the same value for all individuals).

  • when the output directory does not exist, LIAM2 will now try to create it.

  • when debug mode is on, print the position in the random sequence before and after operations which use random numbers.

  • entities are loaded/stored for each period in alphabetical order instead of randomly. This has no influence on the results but produces nicer log files.

  • deprecated the “predictor” keyword. If you need several processes to write to the same variable, you should use procedures instead.


  • using invalid indexes in “global arrays” do not crash anymore if they are properly enclosed in an if() expression. For example if you have an array “by_age” with values for indices from 0 to 99, the following code will now work as expected:

    if(age < 50, by_age[age + 50], 0.5)

    Periodic globals are unaffected (they always return “missing” when out of bounds).

  • fixed link expressions which span 3 (or more) different entities.

  • fixed using show() on a scalar created by summing a “global array”.

  • fixed the progress bar of matching() when the number of individuals is different in the two sets.

Tue, 18 Jun 2013 00:00:00 +0200 <![CDATA[Version 0.6.2 released]]>

Version 0.6.2 released


  • fixed storing a copy of a (declared) field (without any modification) in a temporary “backup” variable. The temporary variable was not a copy but an alias to the same data, so if the field was modified afterwards, the temporary variable was also modified implicitly.

    As an example, the following code failed before the fix:

    # age is a field
    - backup: age
    # modify age (this also modified backup!)
    - age: age + 1
    # failed because "backup" was equal to "age"
    - assertEqual(age, backup + 1)

    This only affected assignment of “pure” fields, not expressions nor temporary variables, for example, the following code worked fine (because backup stores an expression, not a simple field):

    - backup: age * 1
    - age: age + 1
    - assertEqual(age, backup + 1)

    and this code worked too (because temp is a temporary variable, not a field):

    - temp: age + 1
    - backup: temp
    - temp: temp + 1
    - assertEqual(temp, backup + 1)
Wed, 22 May 2013 00:00:00 +0200 <![CDATA[Version 0.6.1 released]]>

Version 0.6.1 released

Miscellaneous improvements

  • when importing an nd-array skip cells with only spaces in addition to empty cells.


  • fixed using non-scalar values (eg fields) as indices of n-dimensional arrays, and generally made indexing n-dimensional arrays more robust.
  • fixed choice which did not refuse to run when the sum of probability is != 1 and the “error” is > 1e-6, as it should. This was the case in past versions but the test was accidentally removed in version 0.5.
  • fixed choice to warn when the sum of probabilities is > 1 (and the error is <= 1e-6). Previously, it only warned if the sum was < 1.
Wed, 27 Mar 2013 00:00:00 +0100 <![CDATA[Version 0.6 released]]>

Version 0.6 released

New features

  • globals handling has been vastly improved:

    • multiple tables: one can now define several tables in globals and not only the “periodic” table.

      These should be imported in the import file and declared in the simulation file in the exact same way that periodic globals are.

      Their usage within a simulation is a bit different though: whereas periodic global variables can be used without prefixing, others globals need to be prefixed with the name of their table. For example, if one has declared a global table named “othertable”:

              - INTFIELD: int
              - FLOATFIELD: float

      its fields can be used like this:

      my_variable: othertable.INTFIELD * 10

      These other global tables need not contain a PERIOD column. When using such a table, LIAM2 will not automatically subtract the “base period” from the index, which means that to access a particular row, you have to use its row index (0 based).

    • n-dimensional globals: in addition to tables, globals can now be n-dimensional arrays. The file format for those should be the same than alignment files. They should be declared like this:

      MYARRAY: {type: float}
    • globals can now be used in all situations instead of only in simple expressions and only for the “current” period. Namely, it makes globals available in: link functions, temporal functions (lag, value_for_period, ...), matching(), new() and in (all the different flavours of) the interactive console.

  • alignment has been vastly improved:

    • align_abs is a new function with the same arguments than align which can be used to align to absolute numbers per category, instead of proportions. Combined with other improvements in this release, this allows maximum flexibility for computing alignment targets on the fly (see below).

    • align on a linked entity (a.k.a immigration): additionally to the arguments of align, align_abs has also an optional “link” argument, which makes it work on the linked entities. The link argument must a one2many link. For example, it can be used to take as many household*s as necessary trying to get as close as possible to a particular distribution of *persons. When the link argument is in effect, the function uses the “Chenard” algorithm.

      In this form, align_abs also supports two extra arguments:

      • secondary_axis: name of an axis which will influence rel_need when the subtotal for that axis is exceeded. See total_by_sex in Chenard. secondary_axis must be one of the alignment columns.
      • errors: if set to ‘carry’, the error for a period (difference between the number of individuals aligned and the target for each category) is stored and added to the target for the next period.
    • renamed the “probabilities” argument of align to “proportions”

    • the “proportions” argument of align() is now much more versatile, as all the following are now accepted:

      • a single scalar, for aligning with a constant proportion.

      • a list of scalars, for aligning with constant proportions per category. (this used to be the only supported format for this argument)

      • an expression returning a single scalar.

      • an expression returning an n-dimensional array. expressions and possible_values will be retrieved from that array, so you can simply use:

        align(score, array_expr)
      • a list of expressions returning scalars [expr1, expr2].

      • a string (in which case, it is treated as a filename). The “fname” argument is still provided for backward compatibility.

    • added an optional “frac_need” argument to align() to control how “fractional needs” are handled. It can take any of three values: “uniform” (default), “cutoff” or “round”.

      • “uniform” draws a random number (u) from an uniform distribution and adds one individual if u < fractional_need. “uniform” is the default behavior.

      • “round” simply rounds needs to the nearest integer. In other words, one individual is added for a category if the fractional need for that category is >= 0.5.

      • “cutoff” tries to match the total need as closely as possible (at the expense of a slight loss of precision for individual categories) by searching for the “cutoff point” that yields:

        count(frac_need >= cutoff) == sum(frac_need)
    • changed the order of align() arguments: proportions is now the second argument, instead of filter, which means you can omit the “fname” or “proportions” keywords and write something like:

      align(score, 'my_csv_file.csv')
    • made align() (and by extension logit_regr) always return False for individuals outside the filter, instead of trying to modify the target variable only where the filter is True. That feature seemed like a good idea on paper but had a very confusing side-effect: the result was different when it was stored in an existing variable than in a new temporary variable.

    • it is no longer possible to use expressions in alignment files. If you need to align on an expression (instead of a simple variable), you should specify the expression in the alignment function. eg:

      align(0.0, fname='al_p_dead.csv', expressions=[gender, age + 1])
  • the result of a groupby can be used in expressions. This can be used, for example, to compute alignment targets on the fly.

  • implemented explore on data files (.h5), so that one can, for example, explore the input dataset.

  • added skip_na (defaults to True) argument to all aggregate functions to specify whether or not missing values (nan for float expressions, -1 for integer expressions) should be ignored.

  • macros can now be used in the interactive console.

  • added “globals” command in the interactive console to list the available globals.

  • added qshow() command to show an expression “textual form” in addition to its value. Example:


    will display:

    grpavg(age): 38.5277057298
  • added optional “pvalues” argument to groupby() to manually provide the “axis” values to compute the expression on, instead of having groupby compute the combination of all the unique values present in the dataset for each column.

Miscellaneous improvements for users

  • improved the documentation, in part thanks to the corrections and suggestions from Alexis Eidelman.

  • added a “known issues” section to the documentation.

  • grpmin and grpmax ignore missing values (nan and -1) by default like other aggregate functions.

  • grpavg ignore -1 values for integer expressions like other aggregate functions.

  • made the operator precedence for “and”, “or” and “not” more sensible, which means that, for example:

    age > 10 and age < 20

    is now equivalent to:

    (age > 10) and (age < 20)

    instead of raising an error.

  • many2one links are now ~30% faster for large datasets.

  • during import, when a column is entirely empty and its type is not specified manually, assume a float column instead of failing to import.

  • allow “id” and “period” columns to be defined explicitly (even though they are still implicit by default).

  • allow “period” in any dimension in alignment files, not only in the last one.

  • disabled all warnings for x/0 and 0/0. This is not an ideal situation, but it is still an improvement because they appeared in LIAM2 code and not in user code and as such confused users more than anything.

  • the “num_periods” argument of lag: lag(age, num_periods) can now be a scalar expression (it must have the same value for all individuals).

  • changed output format of groupby to match input format for alignments.

  • added Warning in grpgini when all values (for the filter) are zeros.

  • when an unrecoverable error happens, save the technical error log to the output directory (for run and explore commands) instead of the directory from where liam2 was run and display on the console where the file has been saved.

  • better error message when an input file has inconsistent row lengths.

  • better error message when using a one2many function in a groupby expression.

Miscellaneous improvements for developers

  • added a “code architecture” section to the documentation.
  • python tracebacks can be re-activated by setting the DEBUG environment variable to True.
  • added a script to automate much of the release process.
  • added source files for creating liam2 bundle (ie add our custom version of notepad++ to the source distribution).
  • updated INSTALL file, and include sections on how to build the documentation and the C extensions.
  • added many tests, fixed a few existing ones and generally greatly improved our test suite.


  • fixed “transposed” option on import. The number of lines to copy was computed on the untransposed data which meant too few data points were copied if the number columns was greater than the number of lines and it crashed if it was smaller.
  • fixed all aggregate functions (except grpcount and grpsum) with a filter argument equal to a simple variable (eg filter=gender) in the presence of “missing” (nan) values in the expression being aggregated: the filter variable was modified.
  • fixed duration() on a simple variable (eg duration(work)): the variable was modified by the function.
  • fixed a nasty bug which made that each variable that needed to be read on disk (lag of more than one period, duration, value_for_period, ...) was read 2 or 3 times instead of just once, greatly slowing down the function.
  • fixed accessing columns for the next-to-last period in the interactive console after a simulation: it was either giving bad results or returning an error.
  • fixed all aggregate functions (except grpcount, grpsum and grpavg which worked) on boolean expressions. This is actually only (remotely) useful for grpgini and grpstd.
  • fixed groupby with both filter and expr arguments.
  • fixed groupby(expr=scalar).
  • fixed sumlink(link, scalar).
  • fixed new(number=...).
  • fixed non-aligned regressions with a filter (it was ignored).
  • fixed the editor shortcuts (to launch liam2) to work when the directory containing the model contains spaces.
  • fixed handling of comments in the first cell of a row in alignments files (the entire row is ignored now).
  • fixed “textual form” of choice expressions when bins or choices are dynamic.
  • fixed using numpy 1.7

Experimental new features

  • implemented optional periodicity for simulation processes.
Mon, 18 Mar 2013 00:00:00 +0100 <![CDATA[Version 0.5.1 released]]>

Version 0.5.1 released

Miscellaneous improvements

  • if there is only one entity defined in a model (like in demo01.yml) and the interactive console is launched, start directly in that entity, instead of requiring the user to set it manually.
  • improved introduction comments in demo models.
  • display whether C extensions are used or not in –versions.
  • use default_entity in demos (from demo03 onward).
  • do not display python version in normal execution but only in –versions.
  • use cx_freeze instead of py2exe to build executables for Windows so that we can use the same script to build executables across platforms and tweaked further our build script to minimise the executable size.
  • compressed as many files as possible in the 32 bit Windows bundle with UPX to make the archive yet smaller (UPX does not support 64 bit executables yet).
  • improved our build system to automate much of the release process.


  • fixed the “explore” command.
  • fixed integer fields on 64 bit platforms other than Windows.
  • fixed demo06: WEMRA is an int now.
  • fixed demo01 introduction comment (bad file name).
Wed, 28 Nov 2012 00:00:00 +0100 <![CDATA[Version 0.5 released]]>

Version 0.5 released

New features

  • added a way to import several files for the same entity. A few comments are in order:
    • Each file can have different data points. eg if you have historical data for some fields data going back to 1950 for some individuals, and other fields going back to only 2000, the import mechanism will merge those data sets.
    • It can also optionally fill missing data points. Currently it only supports filling with the “previous value” (the value the individual had (if any) for that field in a previous period). In the future, we will add more ways to fill those by interpolating existing data. Note that currently only data points which are entirely missing are filled, not those which are set to the special value corresponding to “missing” for the field type (i.e. False for booleans, -1 for integers and “nan” for floats). This will probably change in the future.
    • As a consequence of this new feature, it is now possible to import liam1 files using the “normal” import file syntax.
  • added an optional “default_entity” key to the “simulation” block of simulation files, so that the interactive console starts directly in that entity.
  • added function to compute the Nth percentile: grppercentile(expr, percent[, filter]).
  • implemented an optional filter argument for many functions. The behaviour is different depending on the kind of function:
    • for functions that change an existing variable (clip() and round()), the value for filtered individuals is not modified.
    • for functions which create a new variable (uniform(), normal() and randint()), the value for filtered individuals is the missing value corresponding with the type of the column (-1 for randint(), nan for uniform() and normal()).
    • for aggregate functions (grpmin(), grpmax(), grpstd(), grpmedian() and grppercentile()), the aggregate is computed over the individuals who satisfy the filter.
  • added new functions for testing: assertTrue and assertEqual:
    • assertTrue(expr) evaluates its expression argument and check that it is True.
    • assertEqual(expr1, expr2) evaluates its two expressions and check that they are equal.
  • The behaviour when an assertion fails is configurable through the “assertions” option in the “simulation” block. This option can take three values:
    • “raise”: interrupt the simulation (this is the default).
    • “warn”: display a warning message.
    • “skip”: do not run the assertion at all.
  • added commands to the console:
    • entities: prints the list of available entities.
    • periods: prints the list of available periods for the current entity.
  • added new command line arguments to override paths specified in the simulation file:
    • –input-path: override the input path
    • –input-file: override the input file
    • –output-path: override the output path
    • –output-file: override the output file
  • added –versions command line argument to display versions of all the libraries used.

Miscellaneous improvements

  • performance optimisations:
    • fields which are used in lag expressions are cached (stored in memory) to avoid fetching them from disk. This considerably speeds up lag expressions at the expense of a bit more memory used.
    • implemented a few internal functions in Cython to get C-level performance. This considerably speeds up alignment and groupby expressions, especially when the number of “alignment categories” (the number of possible combinations of values for the variables used to partition) is high. The down side is that if someone wants to recreate liam2 binaries from the source code and benefit from this optimisation (there is a pure-python fallback), he needs to have cython and a C compiler installed.
    • other minor optimisations to groupby and alignments with take or leave filters.
    • slightly sped up initial data loading for very large datasets with a lot of historical data.
  • choices() arguments (options and probabilities) now accept expressions (ie. they can be computed at run time).
  • improved the interactive console:
    • made the interactive console start in the last simulated period by default.
    • changed the behaviour of the “entity” command without argument to print the current entity.
    • the “period” command can now be called without argument to print the current period.
  • added more explicit checks for bad input:
    • check for duplicate headers in alignment files.
    • check all arguments to groupby() are valid instead of only the first one.
    • check for invalid keyword arguments to dump().
    • check for invalid keyword arguments to csv().
    • check the type of arguments to choice().
    • validate globals at load time to make sure the declared globals are actually present in the dataset.
  • disallow strings for the score expression in the matching() function.
  • improved the test coverage: There is still a long way for full test coverage, but the changes in this version is already a first step in the right direction:
    • automated many tests by using the new assertions functions.
    • added more tests.
  • only copy declared globals to the output file, and do not create a “globals” node at all if there is no declared global.
  • manually close input and output files when an error happens during initialisation, so that the user only sees the real error message.
  • globals can be entirely missing from the input file if they are not used in the simulation file.
  • made the usual code clean-ups.


  • fixed typo in the code outputting durations (“hourss” instead of “hours”).
  • fixed a bug which prevented to define constants without quoting them in some cases.
  • fixed a crash when all groups were empty in a groupby(xxx, expr=grpcount(), percent=True).
  • fixed aggregate functions (grpmin, grpmax, grpstd, grpmedian and grppercentile) to accept a scalar as argument (even though it is not very useful to do that).
  • fixed a bug which prevented to use a simulation output file as input in some cases.
Thu, 25 Oct 2012 00:00:00 +0200 <![CDATA[Version 0.4.1 released]]>

Version 0.4.1 released

Miscellaneous improvements

  • validate both import and simulation files, i.e. detect bad structure and invalid and missing keywords.
  • improved error messages (both during import and the simulation), by stripping any information that is not useful to the user. For some messages, we only have a line number and column left, this is not ideal but should be better than before. The technical details are written to a file (error.log) instead.
  • improved “incoherent alignment data” error message when loading an alignment file by changing the wording and adding the path of the file with the error.
  • reorganised bundle files so that there is no confusion between directories for Notepad++ and those of liam2.
  • tweaked Notepad++ configuration:
    • added explore command as F7
    • removed more unnecessary features.


  • disallowed using one2many links like many2one (it was never intended this way and produced wrong results).
  • fixed groupby with a scalar expression (it does not make much sense, but it is better to return the result than to fail).
  • re-enabled the code to show the expressions containing errors where possible (in addition to the error message). This was accidentally removed in a previous version.
  • fixed usage to include the ‘explore’ command.
Fri, 02 Dec 2011 00:00:00 +0100 <![CDATA[Version 0.4 released]]>

Version 0.4 released

New features

  • added grpgini function.
  • added grpmedian function.
  • implemented filter argument in grpsum().
  • implemented N-dimensional alignment (alignment can be done on more than two variables/dimensions in the same file).
  • added keyword arguments to csv():
    • ‘fname’ to allow defining the exact name of the csv file.
    • ‘mode’ to allow appending to a csv file instead of overwriting it.
  • reworked csv() function to support several arguments, like show. It also supports non-table arguments.
  • added ‘skip_shows’ simulation option, to make all show() functions do nothing.
  • allowed expressions in addition to variable names in alignment files.
  • added keyword arguments to dump():
    • ‘missing’ to convert nans into the given value.
    • ‘header’ to determine whether column names should be in the dump or not.
  • improved import functionality:
    • compression is now configurable.
    • any csv file can be transposed, not just globals.
    • globals fields can be selected, renamed and inverted like in normal entities.
  • added “explore” command to the main executable, to launch the interactive console on a completed simulation without re-simulating it.

Miscellaneous improvements

  • expressions do not need to be quoted anymore.
  • reverted init to old semantic: it happens in “start_period - 1”, so that lag(variable_set_in_init) works even for the first period.
  • purge all local variables after each process to lower memory usage.
  • allowed the result of new() to not be stored in a variable.
  • allowed using temporary variables in matching() function.
  • using a string for matching expressions is deprecated.
  • added a tolerance of 1e-6 to the sum of choice’s probabilities to be equal 1.0
  • added explicit message about alignment over and underflows.
  • nicer display for small (< 5ms) and large (>= 1 hour) timings.
  • improved error message on missing parenthesis around operands of boolean operators.
  • improved error message on duplicate fields.
  • improved error message when a variable which is not computed yet is used.
  • added more information to the console log:
    • number of individuals at the start and end of each period.
    • more stats at the end of the simulation.
  • excluded unused components in the executable to make it smaller.


  • fixed logit_regr(align=float).
  • fixed grpavg(bool, filter=cond).
  • fixed groupby(a, b, c, expr=grpsum(d), percent=True).
  • fixed having several grpavg with a filter argument in the same expression.
  • fixed calling the main executable without argument (simply display usage).
  • fixed dump with (some kind of) aggregate values in combination with a filter.
  • fixed void data source.
Fri, 25 Nov 2011 00:00:00 +0100 <![CDATA[Version 0.3 released]]>

Version 0.3 released

New features

  • added ability to import csv files directly with the main executable.

Miscellaneous improvements

  • made periodic globals optional.
  • improved a few sections of the documentation.


  • fixed non-assignment “actions” in interactive console (csv, remove, ...).
  • fixed error_var argument to cont_regr, clip_regr and log_regr.
Wed, 29 Jun 2011 00:00:00 +0200 <![CDATA[Version 0.2.1 released]]>

Version 0.2.1 released

Miscellaneous improvements

  • simplified and cleaned up the demonstration models.
  • improved the error message when a link points to an unknown entity.
  • the evaluator creates fewer internal temporary variables in some cases.


  • added log and exp to the list of available functions (they were already implemented but not usable because of that).
  • fixed log_regr, cont_regr and clip_regr which were comparing their result with 0.5 (like logit_regr when there is no alignment).
  • fixed new() function, which created individuals correctly but in some cases returned values which did not correspond to the ids of the newly created individuals, due to a bug in numpy.
Mon, 20 Jun 2011 00:00:00 +0200 <![CDATA[Presentation of LIAM2 at the 3rd IMA Conference]]>

Presentation of LIAM2 at the 3rd IMA Conference

LIAM2 was presented at the Third General Conference of the International Microsimulation Association, 8-10 June, Stockholm.

You can download the slides here.

Thu, 09 Jun 2011 00:00:00 +0200 <![CDATA[Version 0.2 released]]>

Version 0.2 released

New features

  • added support for retrospective simulation (ie simulating periods for which we already have some data): at the start of each simulated period, if there is any data in the input file for that period, it is “merged” with the result of the last simulated period. If there is any conflict, the data in the input file has priority.

  • added “clone” function which creates new individuals by copying all fields from their “origin” individuals, except for the fields which are given a value manually.

  • added breakpoint function, which launches the interactive console during a simulation. Two more console commands are available in that mode:

    • “s(tep)” to execute the next process
    • “r(esume)” to resume normal execution

    The breakpoint function takes an optional period argument so that it triggers only for that specific period.

  • added “tsum” function, which sums an expression over the whole lifetime of individuals. It returns an integer when summing integer or boolean expressions, and a float for float expressions.

  • implemented using the value of a periodic global at a specific period. That period can be either a constant (eg “MINR[2005]”) or an expression (eg “MINR[period - 10]” or “MINR[year_of_birth + 20]”)

  • added “trunc” function which takes a float expression and returns an int (dropping everything after the decimal point)

Miscellaneous improvements

  • made integer division (int / int) return floats. eg 1/2 = 0.5 instead of 0.

  • processes which do not return any value (csv and show) do not need to be named anymore when they are inside of a procedure.

  • the array used to run the first period is constructed by merging the individuals present in all previous periods.

  • print timing for sub-processes in procedures. This is quite verbose but makes debugging performance problems/regressions easier.

  • made error messages more understandable in some cases.

  • manually flush the “console” output every time we write to it, not only within the interactive console, as some environments (namely when using the notepad++ bundle) do not flush the buffer themselves.

  • disable compression of the output/simulation file, as it hurts performance quite a bit (the simulation time can be increased by more than 60%). Previously, it was using the same compression settings as the input file.

  • allowed align() to work on a constant. eg:

    align(0.0, fname='al_p_dead_m.csv')
  • made the “tavg” function work with boolean and float expressions in addition to integer expressions

  • allowed links to be used in expression given in the “new” function to initialise the fields of the new individuals.

  • using “__parent__” in the new() function is no longer necessary.

  • made the “init” section optional (it was never intended to be mandatory).

  • added progress bar for copying table.

  • optimised some parts for speed, making the whole simulation roughly as fast as 0.1 even though more work is done.


  • fixed “tavg” function:
    • the result was wrong because the number of values (used in the division) was one less than it should.
    • it yielded “random” values when some individuals were present in a past period, but not in the current period.
  • fixed “duration” function:
    • it crashed when a past period contained no individuals.
    • it yielded “random” values when some individuals were present in a past period, but not in the current period.
  • fixed “many2one” links returning seemingly random values instead of “missing” when they were pointing to an individual which was not present anymore (usually because the individual was dead).
  • fixed min/max functions.
  • fields which are not given an explicit value in new() are initialised to missing, instead of 0.
  • the result of the new() function (which returns the id of the newly created individuals) is now -1 (instead of 0) for parents which are not in the filter.
  • fixed some expressions crashing when used within a lag.
  • fixed the progress bar to display correctly even when there are only very few iterations.
Tue, 07 Jun 2011 00:00:00 +0200