si2.m

很多matlab的源代码

function Y = si2(x,a)
% SI2   Integral of [sin(at)/(at)]^2 .
%
%	Y = SI2(X,A) Computes integral of [sin(At)/(At)]^2 over [0, X] 
%
%	SI2 (with no input arguments) invokes the following example:
%
%	% How much energy is contained in the central lobe [-1,1] of sinc(t)?
%	% Since E=sinc^2(t) is even, we find the energy in half the mainlobe 
%	% and double result. NOTE that sinc(t) = sin(pi*t)/(pi*t)
%	>>e = 2*si2(1,pi) 
%	% Plot the area under sinc(t) and sinc^2(t) over [0 5]
%     	  >>t = 0:0.05:5;
%     	  >>x1 = si(t,pi);
%     	  >>x2 = si2(t,pi);
%     	  >>plot(t,x1,t,x2),grid


% 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 si2,disp('Strike a key to see results of the examples')
pause,e=2*si2(1,pi),t=0:.05:5;x1=si(t,pi);x2=si2(t,pi);
 vx=matverch;
 if vx < 4, eval('clg');else,eval('clf');end
plot(t,x1,t,x2),grid,return,end

if nargin<2,a=1;end
z=x+(x==0);y=abs(2*a*z);
Y1=si(y);
y1=rem(y,2*pi);
Y=(x~=0).*sign(x).*(Y1+(cos(y1)-1)./y)/a;