why result is zero?

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Habib
Habib 2015-3-10
评论： Torsten 2015-3-10
Hi everybody. In second "for" nesting loop, I want to use Trapz command (numerical integration) for integration from an N*N matrix (u_2) but I got zero answer? What is wrong? I hope one give an answer.
clc
clear all
close all
aa=3e-2;
E0=10000;
z=0.42;
L=z;
N=100;
lambda=1030e-9;
k=2*pi/lambda;
w0=0.0001;
zr=pi*w0^2/lambda;
R=z*(1+(zr/z)^2);
w=w0*sqrt(1+(z/zr)^2);
D1=linspace(-aa/2,aa/2,N);
[x,y]=meshgrid(D1,D1);
b=(lambda*L)/(N*aa);
D2=linspace(-b/2,b/2,N);
[xx,yy]=meshgrid(D2,D2);
RR=1.5;
u1=ones(size(x));
u_2=u1;
u2=ones(size(xx));
[teta,r]=cart2pol(x,y);
[teta1,rr] = cart2pol(xx,yy);
for i=1:N
for j=1:N
u1(i,j)=E0*(r(i,j)/w)*exp(-(r(i,j)/w).^2);
end
end
for i=1:N
for j=1:N
u_2(i,j)=u1(i,j)*besselj(1,-k*r(i,j)*rr(i,j))*exp(-1i*k*rr(i,j)^2/(L*w^2))*cos(teta1(i,j));
u2(i,j)=trapz(u_2(i,j));
end
end
  2 个评论
Habib
Habib 2015-3-10
Thank you for your answer.
I read it, but i couldn't understand what is wrong. Now, what must I do? how i can fixed it?
Torsten
Torsten 2015-3-10
x = -3:.1:3;
y = -5:.1:5;
[X,Y] = meshgrid(x,y);
F = X.^2 + Y.^2;
I = trapz(y,trapz(x,F,2));
integrates the function f(x,y)=x^2+y^2 over the rectangle [-3:3]x[-5:5].
Now insert your function and your domain of integration.
Best wishes
Torsten.

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采纳的回答

Torsten
Torsten 2015-3-10
Take a look at the chapter "Multiple numerical integrations" under
http://de.mathworks.com/help/matlab/ref/trapz.html
to see what is wrong with your call to trapz.
Best wishes
Torsten.

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