How can I pass a matrix as a parameter into a C-MEX S-function?

How can I pass a matrix as a parameter into a C-MEX S-function?

Answer 1

[MathWorks Support Team]

In order to pass a matrix as a parameter into a C-MEX S-function, you want to use the ssGetSFcnParam macro to get the parameter as follows:

#define PARAM_ARG ssGetSFcnParam(S, 0)                 %zero will be the parameter index

Then, in mdlOutputs, you can do the following to access the parameter:

real_T      *p     = mxGetPr(PARAM_ARG);

You would then index into each element of "p" to get each element of the matrix.

NOTE: Matrices are stored in column major order in S-functions. So you will have to access each matrix element by one index not two indices.For example, if the parameter is a [2x2] matrix

             -          - 

            | p[0]  p[2] |

            | p[1]  p[3] |

            -           -

            Output elements are stored as follows:

                p[0] --> row = 0, col = 0

                p[1] --> row = 1, col = 0

                p[2] --> row = 0, col = 1

                p[3] --> row = 1, col = 1

For a more detailed decription of how S-functions handle matrices, see the sfun_matadd.c example that is available in the $MATLAB/simulink/src directory (till release MATLAB R2009a).

In the MATLAB R2012b release, can refer to the following SFunction Demo :

>> sfcndemo_stvmgmain

which, implements a time-varying matrix gain