External Interfaces/API

Calling Functions from Fortran MEX-Files

It's possible to call MATLAB functions, operators, M-files, and even other MEX-files from within your Fortran source code by using the API function mexCallMATLAB. This example creates an mxArray, passes various pointers to a subfunction to acquire data, and calls mexCallMATLAB to calculate the sine function and plot the results.

C     $ Revision: 1.8 $
C 
================================================================
C     
C     sincall.f
C
C     Example for illustrating how to use mexCallMATLAB.
C     
C     Creates an mxArray and passes its associated pointers (in
C     this demo, only pointer to its real part, pointer to number
C     of rows, pointer to number of columns) to subfunction fill()
C     to get data filled up, then calls mexCallMATLAB to calculate
C     sin function and plot the result.
C
C     NOTE: The subfunction fill() is in the file called fill.f.
C
C     This is a MEX-file for MATLAB.
C     Copyright (c) 1984-2000 The MathWorks, Inc.
C     
C ==============================================================

C     Gateway subroutine

      subroutine mexFunction(nlhs, plhs, nrhs, prhs)
      integer nlhs, nrhs
C---------------------------------------------------------------
C     (pointer) Replace integer by integer*8 on the DEC Alpha  
C     platform.
C
      integer plhs(*), prhs(*)
      integer rhs(1), lhs(1)
      integer mxGetPr, mxCreateFull
C---------------------------------------------------------------
C
      integer m, n, max
      
C     initializition
      m=1
      n=1
      max=1000

      rhs(1) = mxCreateFull(max, 1, 0)
 
C     Pass the pointer and variable and let fill() fill up data.
      call fill(%val(mxGetPr(rhs(1))), m, n, max)
      call mxSetM(rhs(1), m)
      call mxSetN(rhs(1), n)

      call mexCallMATLAB(1, lhs, 1, rhs, 'sin')
      call mexCallMATLAB(0, NULL, 1, lhs, 'plot')

C     Clean up the unfreed memory after calling mexCallMATLAB.
      call mxFreeMatrix(rhs(1))
      call mxFreeMatrix(lhs(1))

      return
      end  

C     $ Revision: 1.3 $
C 
================================================================
C     
C     fill.f
C     This is the subfunction called by sincall that fills the 
C     mxArray with data. Your version of fill can load your data
C     however you would like.
C
C     This is a MEX-file for MATLAB.
C     Copyright (c) 1984-2000 The MathWorks, Inc. 
C     
C 
================================================================
C     Subroutine for filling up data.

      subroutine fill(pr, m, n, max)
      
      real*8  pr(*)
      integer i, m, n, max
     
      m=max/2
      n=1
      do 10 i=1,m
 10      pr(i)=i*(4*3.1415926/max)

      return
      end

It is possible to use mexCallMATLAB (or any other API routine) from within your computational Fortran subroutine. Note that you can only call most MATLAB functions with double-precision data. M-functions that perform computations, like eig, will not work correctly with data that is not double precision.

Running this example

sincall

displays the results

Note    It is possible to generate an object of type mxUNKNOWN_CLASS using mexCallMATLAB. See the example below.

The following example creates an M-file that returns two variables but only assigns one of them a value.

    function [a,b]=foo[c]
    a=2*c;

MATLAB displays the following warning message.

    Warning: One or more output arguments not assigned during call
    to 'foo'.

If you then call foo using mexCallMATLAB, the unassigned output variable will now be of type mxUNKNOWN_CLASS.

Handling Sparse Matrices

Advanced Topics