External Interfaces/API

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: 1.9 $
  C==============================================================
  =
  
  C     The gateway subroutine
        subroutine mexfunction(nlhs, plhs, nrhs, prhs)
  C--------------------------------------------------------------
  -
  C     (pointer) Replace integer by integer*8 on the DEC Alpha
  C     64-bit platform
  
        integer plhs(*), prhs(*)
        integer pr_in, pr_out
        integer mxGetPr, mxCreateDoubleMatrix
  C--------------------------------------------------------------
  -
  
        integer nlhs, nrhs, mxGetM, mxGetN
        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: 1.9 $
  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