basic signal processing functions

h.fft(x,N,W) h.ifft(x,N) h.conv(x,y) h.freqz(b,a,N,W) h.interp(x,N) h.decimate(x,N)

Re-implement some basic DSP related functions. Not so powerful as matlab built-in ones, but could give an ideal how these functions work.

mydsp.m: implementation of the functions.
use_mydsp.m: examples of how to use the functions; accuracy also verified by comparing the output with Mablab built-in funcs.