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==============================================================
  =
  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     $Revision: 1.9 $
  C ==============================================================
  
  C     The gateway routine
        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 rhs(1), lhs(1)
        integer mxGetPr, mxCreateDoubleMatrix
  C--------------------------------------------------------------
  -
  
        integer nlhs, nrhs
        integer m, n, max
        
  C     initializition
        m = 1
        n = 1
        max = 1000
  
        rhs(1) = mxCreateDoubleMatrix(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 mxDestroyArray(rhs(1))
        call mxDestroyArray(lhs(1))
  
        return
        end
  

This is the subroutine that sincall calls to fill the mxArray with data.

• 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     $Revision: 1.9 $
  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