Need help in evaluating integral with quad

11 vues (au cours des 30 derniers jours)
Raghav
Raghav le 10 Mar 2011
Hi,I need to numerically evaluate an integral,for different values of a parameter,and store these in a vector.The integral is:
f(theta)=integral of(exp(-2x)*sin(2xsin(theta/2))dx, x running from 0 to 2 I am trying to attempt this with quad using the anonymous function approach.I coded it thus,
theta=0.01:0.1:2*pi-0.01;
f=@(x,th)(exp(-0.5*x)*sin(x*2*sin((th)/2)));
for i=1:length(theta)
th=theta(i);
born(i)=quad(@(x)f(x,th),0,2);
end;
I cannot understand why I get the error
??? Error using ==> mtimes
Inner matrix dimensions must agree.
Error in ==> @(x,th)(exp(-0.5*x)*sin(x*2*sin((th)/2)))
Error in ==> @(x)f(x,th)
Error in ==> quad at 77
y = f(x, varargin{:});
Error in ==> born_integral at 8
born(i)=quad(@(x)f(x,th),0,2);
Is there a way to make it work with quad or a similiar function ? (I'll try numerical integration algorithms as a last resort) Thanks in advance.
  1 commentaire
John D'Errico
John D'Errico le 10 Mar 2011
Quad IS a numerical integration algorithm!!!!!

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Réponse acceptée

Paulo Silva
Paulo Silva le 10 Mar 2011
Just a dot missing from the second line, before *sin
theta=0.01:0.1:2*pi-0.01;
f=@(x,th)(exp(-0.5*x).*sin(x*2*sin((th)/2)));
for i=1:length(theta)
th=theta(i);
born(i)=quad(@(x)f(x,th),0,2);
end

Plus de réponses (1)

Matt Fig
Matt Fig le 10 Mar 2011
Or, you can do it in one shot with QUADV:
th = 0.01:0.1:2*pi-0.01;
f = @(x)(exp(-0.5*x).*sin(x*2*sin((th)/2)));
born = quadv(f,0,2);

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