Well I still use Mathcad 2001, as I missed 2001i and I am not willing to accept a softlock to a certain computer hardware as with Mathcad 11 and newer.
So Mathcad 2001 was shipped with a crippled "light" version of a simulation software "VisSim Comm LE", with some examples how to use Mathcad calculations for a controlling modell running with VisSim.
In general, with such continous simulation software like SIMULINK part of Matlab/Simulink, there is the option to create a "C" code to put the intelligence of the controlling algorithm of the home-made simulation into an industrial controller ( with earlier versions of Scilab, there was a internal creation of C code too, but nowadays never again).
So if you got such code of just few hundreds of lines, without much overhead, of course you MIGHT include a mathematical library if "ROM/RAM space" is not the problem.
So in general, MatCad and continous simulations are for DEVELOPMENT, in the labs,
while the "real code" on the embedded application is just C-code and you have to replace the intelligence of Mathcad by your "own" library or a commercial library. So an FFT should be no problem to do with a C library without expensive tools.
The other aspect is the ability of Mathcad for symbolic calculations - which is not possible with Matlab and Scilab.
But this feature is not usual for industry applications, where you run software which was created to work with parameters with "solved" the problem....
So advice: Solve your problems with Mathcad, and then TRANSFER the solution to your target system without Mathcad.
With Matlab/Simulink AND Scilab/Scicos, you "might" use it both for development and distribution: With Matlab you supply the "slim" C code ( so that you avoid the full license fee for distributing Matlab with each application), with Scilab you run a full version on a windows or Linux system ( as there is no license fee )
Might you tell us about your appliation ?!
Sincerely
Rolf