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wmat files are used to store weight matrices in the MatrixMarket format, which can be exchanged easily with MATLAB and other software (http://en.wikipedia.org/wiki/Matrix_Market_exchange_formats). Since in many cases connection matrices are sparse, Auryn uses the coordinate real format, which needs to be kept in row major order, since it directly maps Auryn's internal sparse matrix format SimpleMatrix.

File structure

The header of a typical weight matrix looks the following:

%%MatrixMarket matrix coordinate real general
% Auryn weight matrix. Has to be kept in row major order for load operation.
% Connection name: Poisson->E
% Locked range: 8
%
1000 4000 49952
1 57 6.971942e-02
1 129 6.517706e-02
1 233 6.546227e-02
1 385 5.322644e-02
1 457 7.060073e-02
1 617 6.956130e-02
...

It contains some generic header lines and comments followed by the Connection name (which is not read upon load) and some additional information to identify from on how many ranks the weight matrix was residing. The first line without percent sign specifies the dimensionality followed by the number of nonzero elements. The latter is used by SimpleMatrix to reserve exactly the right amount of memory. After that, the existing connection elements are listed in the format: row (from) column (to) value.

Nota bene: Cells in the wmat file are indexed starting from 1 (unlike everywhere else in Auryn, where we adapt the C convention and start numbering arrays with 0).