interpol.m

很多matlab的源代码

function yy = interpol(f,ty,n,r)
% INTERPOL Signal Interpolation.
%
%	Y = INTERPOL(F,TY,N,R) interpolates signal F to N-fold sequence 
%	TY = interpolation algorithm which can be one of the following:
% 	'c'(onstant, 'l'(inear), 's'(inc), 'r'(aised cosine), 'd'(ft), 'z'(ero) 
%	R = additional parameter if TY = 'r' (DEFAULT: R = 0.5)
%	Y = interpolated signal with N times length(F) [Default: N = 4] 
%
%	Plots interpolated signal vs index if NO OUTPUT ARGUMENT SPECIFIED 
%
%       INTERPOL (with no input arguments) invokes the following example:
%
%	% Generate a coarse sine wave at 0.2s intervals and interpolate to 
%	% 4 times its length using sinc interpolation 
%         >>ta = 0:0.2:1;
%         >>xa = sin(pi*ta);
%         >>interpol(xa,'sinc')   % N=4 is default


% ADSP Toolbox: Version 2.0 
% For use with "Analog and Digital Signal Processing", 2nd Ed.
% Published by PWS Publishing Co.
%
% Ashok Ambardar, EE Dept. MTU, Houghton, MI 49931, USA
% http://www.ee.mtu/faculty/akambard.html
% e-mail: [e-mail]
% Copyright (c) 1998



if nargin==0,help interpol,disp('Strike a key to see results of the example')
pause,ta=0:.2:1;xa=sin(pi*ta);interpol(xa,'sinc');return,end

if nargin<4,r=0.5;end,
if nargin<3,n=4;end,
if nargin<2,ty='z';end
if n==1,y=f;return,end %Trivial case
r=r-5.5*eps;ty=ty(1);
n0=n-1;[mm,nn]=size(f);m=max(mm,nn);
if mm==1,f=f(:);end
if n0 < 1, error('interpolation factor must be a positive integer'),end
l=n*m;x=zeros(l,1);x(1:n:l)=f;
if ty=='c',d=0;t=0:1/n:1;xi=ones(1,n);end %xi=rect(t-.5);
if ty=='l',d=n;t=-1:1/n:1;xi=tri(t);end
if ty=='s',d=m*n;t=-m:1/n:m;xi=sinc(t);end
if ty=='r',d=m*n;t=-m:1/n:m;xi=sinc(t).*cos(pi*r*t)./(1-4*r*r*t.*t);end
if ty=='d'
i=fix(m/2)+1;a=fft(f);a=[a(1:i);zeros(n0*m,1);a(i+1:m)];
if rem(m,2)==0,
a(i)=a(i)/2;a(i+m*n0)=a(i);end,y=n*real(ifft(a));
elseif ty=='z'
y=[f.';zeros(n0,m)];y=y(:);
else
y=conv(x,xi);y=y(d+1:d+m*n);
end
y=y.*(abs(y)>50*eps);
if mm==1,y=y.';end
if nargout==0,subplot
 vx=matverch;
 if vx < 4, eval('clg');else,eval('clf');end
l1=(0:l-1)';dtplot(l1,y,'o'),hold on,
plot(0:n:l-1,f,'*'),axesn,hold off
else,
yy=y;
end