fsform.m

精通Matlab综合辅导与指南-源程序随书带的光盘

function [a,b,ao]=fsform(c,d,co)
%FSFORM Fourier Series Format Conversion.
% Kn=FSFORM(An,Bn,Ao) converts the trigonometric FS with
% An being the COSINE and Bn being the SINE coefficients to
% the complex exponential FS with coefficients Kn.
% Ao is the DC component and An, Bn and Ao are assumed to be real.
%
% [Kn,i]=FSFORM(An,Bn,Ao) returns the index vector i that
% identifies the harmonic number of each element of Kn.
%
% [An,Bn,Ao]=FSFORM(Kn) does the reverse format conversion.

% D.C. Hanselman, University of Maine, Orono, ME 04469
% 1/12/95
% Copyright (c) 1996 by Prentice-Hall, Inc. 

nc=length(c);
if nargin==1		% complex exp --> trig form
 if rem(nc-1,2)|(nc==1)
  error('Number of elements in K must be odd and greater than 1')
 end
 nn=(nc+3)/2;
 a=2*real(c(nn:nc));
 b=-2*imag(c(nn:nc));
 ao=real(c(nn-1));
elseif nargin==3	% trig form --> complex exp form
 nd=length(d);
 if nc~=nd,
  error('A and B must be the same length')
 end
 a=0.5*(c-sqrt(-1)*d);
 a=[conj(a(nc:-1:1)) co(1) a];
 b=-nc:nc;
else
 error('Improper number of input arguments.')
end