Dynamically Allocating Memory :: Creating Fortran MEX-Files (External Interfaces)

External Interfaces

Dynamically Allocating Memory

It is possible to allocate memory dynamically in a Fortran MEX-file, but you must use %val to do it. This example takes an input matrix of real data and doubles each of its elements.

C==============================================================
=
C     dblmat.f
C     Example for illustrating how to use %val.
C     Doubles the input matrix. The demo only handles real part
C     of input.
C
C     NOTE: If your Fortran compiler does not support %val, 
C     use mxCopy_routine.
C     NOTE: The subroutine compute() is in the file called
C     compute.f. 
C
C     This is a MEX-file for MATLAB.
C     Copyright (c) 1984-2000 The MathWorks, Inc.
C     $Revision: 1.13 $
C==============================================================
=

C     The gateway subroutine
      subroutine mexfunction(nlhs, plhs, nrhs, prhs)

      integer mxGetPr, mxCreateDoubleMatrix
      integer mxGetM, mxGetN
      integer nlhs, nrhs, plhs(*), prhs(*)
      integer pr_in, pr_out
      integer m_in, n_in, size

      if(nrhs .ne. 1) then
         call mexErrMsgTxt('One input required.')
      endif
      if(nlhs .gt. 1) then
         call mexErrMsgTxt('Less than one output required.')
      endif
         
      m_in = mxGetM(prhs(1))
      n_in = mxGetN(prhs(1))
      size = m_in * n_in
      pr_in = mxGetPr(prhs(1))
      plhs(1) = mxCreateDoubleMatrix(m_in, n_in, 0)
      pr_out = mxGetPr(plhs(1))

C     Call the computational routine.
      call compute(%val(pr_out), %val(pr_in), size)

      return
      end

This is the subroutine that dblmat calls to double the input matrix.

C==============================================================
=
C     compute.f
C
C     This subroutine doubles the input matrix. Your version of 
C     compute() may do whaveter you would like it to do.
C
C     This is a MEX-file for MATLAB.
C     Copyright (c) 1984-2000 The MathWorks, Inc. 
C     $Revision: 1.3 $
C==============================================================
=

C     Computational subroutine
      subroutine compute(out_mat, in_mat, size)
      integer size, i
      real*8  out_mat(*), in_mat(*)

      do 10 i=1,size
         out_mat(i) = 2*in_mat(i)
 10   continue

      return
      end

For an input 2-by-3 matrix

```
x = [1 2 3; 4 5 6];
```

typing

```
y = dblmat(x)
```

yields

y =
     2     4     6
     8    10    12

Note The dblmat.f example, as well as fulltosparse.f and sincall.f, are split into two parts, the gateway and the computational subroutine, because of restrictions in some compilers.

Handling Complex Data Handling Sparse Matrices