User`s manual

3 Creating Fortran MEX-Files

3-8

When a MEX-file completes its task, it returns control to MATLAB. Any

MATLAB arrays that are created by the MEX-file that are not returned to

MATLAB through the left-hand side arguments are automatically destroyed.

The %val Construct

The %val construct is supported by most, but not all, Fortran compilers.

DIGITAL Visual Fortran does support the construct.

%val causes the value of

the variable, rather than the address of the variable, to be passed to the

subroutine. If you are using a Fortran compiler that does not support the

%val

construct, you must copy the array values into a temporary true Fortran array

using special routines. For example, consider a gateway routine that calls its

computational routine,

yprime, by

call yprime(%val(yp), %val(t), %val(y))

If your Fortran compiler does not support the %val construct, you would replace

the call to the computational subroutine with

C Copy array pointers to local arrays.

call mxCopyPtrToReal8(t, tr, 1)

call mxCopyPtrToReal8(y, yr, 4)

C Call the computational subroutine.

call yprime(ypr, tr, yr)

C Copy local array to output array pointer.

call mxCopyReal8ToPtr(ypr, yp, 4)

You must also add the following declaration line to the top of the gateway

routine.

real*8 ypr(4), tr, yr(4)

Note that if you use mxCopyPtrToReal8 or any of the other mxCopy__ routines,

the size of the arrays declared in the Fortran gateway routine must be greater

than or equal to the size of the inputs to the MEX-file coming in from MATLAB.

Otherwise

mxCopyPtrToReal8 will not work correctly.