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Sassy Modelling Helpers Gem

This is a set of Ruby scripts for creating ODE models that can be used in SASSy, a MATLAB-based software for performing sensitivity analysis on dynamical systems models, e.g. in mathematical biology. Especially together with converters like VFGen and SBFC, this tool is helpful when creating command-line scripted parameter sweeps or when using different software packages for analysing a model.

So far, it can:

  • Read models from XPP format used e.g. in XPP-Auto
  • Read models and parameter files in SASSy's own format
  • Write these models to MATLAB/SASSy/XPP/SBML/VFGen/C++ format
  • Merge two models into one by re-defining parameters as species (this requires writing a Ruby script)
  • Change parameters in a model on the command line for quick scripted parameter sweeps.
  • Replace parameters by their numerical values (useful when using together with VFGen to output Auto models).


### Quick install

While this is in gem format and uses Bundler, I have not uploaded it to something like Rubygems yet.

Therefore, the simplest way to use it might well be to clone the repository to your computer, and install the dependencies like this:

$ git clone
# ...
$ cd sassy-helpers
$ bundle install
# ...

To see if everything works ok, you can run

bundle exec rspec

to run the tests. Some example models are included in spec/testmodels.

You can then install the gem by running

rake install

Should this not work...

You need to have Ruby at version > 1.9.3 and a relatively recent version of bundler. On OSX 10.6 (like my system), this isn't necessarily the case by default.

The easiest way to get these is using RVM.

In short, run something like

\curl -L | bash -s stable --ruby
rvm install 1.9.3
rvm use 1.9.3
gem install bundler

# ... go to the sassy-helpers directory

# this installs dependencies
bundle install

Again, you can install the gem by running

rake install


In the sassy-helpers directory, there is a bin directory, which contains the sassyconvert script.

WARNING: This script will not ask to overwrite outputs if they already exist, but rather just go and do so. Make backups of your ode and model files (or write to a different location).

You can use it to convert back and forth between different formats:

$ bin/sassyconvert spec/testmodels/ode/cellcycle_gerard10_5var.ode cellcycle_gerard10_5var

will create three files:


You can also convert these back to ode:

$ sassyconvert cellcycle_gerard10_5var cellcycle.ode --informat sassy --outformat xpp

This will create cellcycle.ode. Note that this file is not necessarily identical with the original ode file it came from: the xpp format has a few fuzzy rules, and we don't remember the exact way this was implemented in the input file (we do remember extra lines with an @ or " in the beginning though).

It is possible to change parameter values in the output model, the following sets the parameter GF to 2 (note: no spaces allowed in the assignment statement -- GF = 2 rather than GF=2 will give an error).

$ sassyconvert cellcycle_gerard10_5var cellcycle.ode --informat sassy --outformat xpp --set GF=2.0

Running the script with option --help will show further options.


Note that due to the limitations of what SASSy can do, we are limited to a subset of XPP's (and eventually SBML's) features:

  • Models can only have scalar or rate rules
  • No SBML-style reactions are supported
  • Formulas must be in MATLAB/Octave-friendly format
  • Not all of XPP's features are supported (boundary conditions, int{...}, etc.)

Some sanity-checking is done on the models, but we don't actually parse formulas (match braces, check for existence of functions, etc.).

When things aren't recognized, you can see warnings like

[W] unmatched xpp line: f(u)=1/(1+exp(-( )))

and then possibly the model won't validate.


... stuff I plan to add

  • VFGen XML format input


Sassy Dynamic Systems Modelling conversion scripts



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