Question

I am computing a Fourier transformation in MATLAB, when computing coefficients C[0] and C[n*f0], I got pretty nasty result because MATLAB doesn’t recognize my variable “n” as integer. I currently compute with “n” as a symbolic variable (syms n;). How to change symbolic n to symbolic integer n?

Answer 1

Looking at the MATLAB documenation, to add the assumption “n is integer” in R2008b or later, you have to write

evalin(symengine,'assume(n,Type::Integer)')

This answers your question, however, I’m not really sure it solves your problem.

When you do a Fourier transform, you are performing a heavy numeric operation on your data, consequently all variables involved in that need to have concrete values. Your n probably should be an integer, but not just by type, it should contain an actual number. If you declare it using syms, it will potentially not contain a number, so you be sure you really need the symbolic toolbox!

If you do, and n is the result of a calculation that yield one specific integer, you can convert it to normal numerical form using uint32(n) or similar, see the help on conversions, e.g.

Y = fft(X,uint32(n))

Update: The error message you give in the comment implies that your n is in fact not an integer… I doubt you will be able to use it with fft.