FAQ

Frequently Asked Questions about Topographica

Here we collect together some answers to general questions about Topographica. If you have a problem that isn’t answered below, please feel free to ask us (either in one of our forums, or by email).

1. Q: How can I get access to the actual data shown in the various plots, etc.?

   A: The main objects in the simulation can be accessed through the topo.sim attribute. For instance, if you have a sheet named 'V1', it can be accessed as topo.sim.V1. From there the projections, weights, etc. for that unit can be obtained. See the Command line section of the user manual for more information, including how to plot such data manually.

2. Q: After upgrading Topographica or editing some of its files, I get errors when loading a saved snapshot.

   A: As of 0.9.5, Topographica saves the state by using Python’s pickling procedure, which saves everything in the current simulation. The disadvantage of this approach is that changes in the definition of any of the classes used (apart from changing parameter values or strictly adding code) can cause the reloading to fail. Whenever possible, we provide legacy snapshot support that maps from the old definition into the new one, and so snapshots should continue to be loadable. However, if you have trouble with a particular file, please file a bug report so that we can extend the legacy support to be able to load it. We may eventually set up an XML or HDF5-based archival storage format, but this is difficult to achieve with the fast pace of Topographica development.

3. Q: What models or algorithms does Topographica support?

   A: Topographica is built in a highly modular fashion, and thus it can support an effectively infinite number of algorithms with little or no change to the underlying code. For instance, there is no particular Topographica component that implements the SOM algorithm – instead, a SOM network like examples/som_retinotopy.ty is simply built from:

   1. An input pattern specified from a large library of possible PatternGenerators
   2. A general-purpose GeneratorSheet for presenting input patterns
   3. A general-purpose weight projection class CFProjection
   4. A general-purpose array of units CFSheet
   5. A specialized transfer function (KernelMax) that picks a winning unit and activates the rest according to a user-specified kernel function (also implemented as a PatternGenerator).

   This approach makes it simple to change specific aspects of a model (e.g. to choose a different PatternGenerator for the kernel function) without necessarily requiring any new code, as long as the new function has already been written for any previous model. For this example, only the KernelMax function (about 50 lines of Python code) was added specifically for supporting SOM; the other components were all already used in a wide variety of other models.

4. Q: I think I’ve found a problem with Topographica. What should I do now?

   A: Topographica is continuously changing to support active research, so problems can occur. To be sure you have found a problem with Topographica itself, and to help us fix it quickly, please follow our guidelines for Reporting specific problems with Topographica.

5. Q: pip failed while processing dependencies. What can I do now?

   A: pip can sometimes encounter problems while processing dependencies. In such cases, installation will stop at the failed dependency, so it is usually straightforward to identify and fix the problem. Below we list some possibilities for solving pip problems:

   • pip dependency-processing problems can sometimes be solved by installing the individual dependencies before running pip install topographica: pip install numpy; pip install PIL (then, optionally, other recommended dependencies). Once these are installed, repeat the pip install topographica command.
   • Binaries of Topographica’s required dependencies (NumPy and PIL) as well as optional dependencies (MatPlotLib, gmpy, SciPy) are available for many platforms, using the native package manager for your platform (if available) or self-installing .exe files (for Windows). Once installed, repeat the pip install topographica command. Note that it’s not always obvious how to make sure that separate installations like this all use the same copy of Python as Topographica is using, but doing so is necessary for this approach to work.
   • If a binary is not available for your platform, you should check the dependency’s installation instructions for your platform. Usually, you will need to make sure that you have typical code-building tools (e.g. a C/C++ compiler). Your distribution will usually have such tools available, e.g. the “build-essential” package on Ubuntu or Xcode on Mac. You will also need the Python headers, for which it might be necessary to install your distribution’s “python-dev” or “python-devel” package.

6. Q: On my Mac, the GUI windows take a long time to refresh, seeming to bounce around for a while. Why is this?

   A: There is a bug in some versions of Tcl/Tk on OS X that causes Tkinter to perform very slowly. You could try installing a newer version of Tcl/Tk (e.g. ActiveTcl), but you would need to make sure your copy of Python is built against it. Please feel free to contact Topographica’s developers if you would like more help with this problem.