Classic Fourier Series

[Snorre]

Hello Salvo,

you're right. In general, changing the integration interval is like shifting the time function, which should result in different phase information only (the magnitudes shall stay the same).
But that holds only for periodic functions (a basic assumption of fourier transformations). If you transform f(t):=t² in -pi..pi, you're assuming f is an endless repetition of the cup-like part pi²..0..pi² (in ASCII-art: ...uuuu...), if you do it on 0..2pi you're assuming f is an endless repetition of the raising 0..pi²..4pi² chunk (in ASCII-art: ...////...) -- these are two different time functions.

You could put your choose box in a non-exported (private) PPL-function within the same program and call it like <programname>.<funcname>:

Code:

ChooseInterval()
BEGIN
  LOCAL choice;
  CHOOSE(choice,...);
  RETURN choice;
END;

#cas
fourcoeff(...):=
BEGIN
  ...
  IF MYFOURIERPROG.ChooseInterval()=1 THEN
   ak:=...-pi..pi...
  ELSE
   ak:=...0..2*pi...
  END;
  ...
END;
#end