MATLAB: Matrix dimensions must agree.

matrix

i dont where the wrong in this equation:

function F = Fint(a)

F = quad(@(x)(x.*sin(x))./(1-(2.*a.*cos(x))+a.^(2)),0,pi);

end

where the output i got is

Matrix dimensions must agree.

Error in Fint>@(x)(x.*sin(x))./(1-(2.*a.*cos(x))+a.^(2)) (line 2)

F = quad(@(x)(x.*sin(x))./(1-(2.*a.*cos(x))+a.^(2)),0,pi);

Best Answer

To integrate a vector, use the quadv (link) function.

If you have R2012a or later, use integral (link) with the 'ArrayValued' option instead.

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MATLAB: Need help in evaluating integral with quad

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

MATLAB: Problem with integrals

A very good question. You need to use QUADV here instead of QUAD.

quadv(@(x) exp(x.^2).*quad(@(z) exp(z.^2),-2,x),-2,2)

QUAD expects vector inputs and outputs, and so when it goes to evaluate the inner QUAD, it sends in a vector which is why you get that error.

Notice that QUAD will error on a problem like this one here below for the same reason (but QUADV will work fine):

quad(@(x) det([x 1; 1 1]),0,1)

QUADV does it without trying to send in vectors.

Just as a sanity check, compare what you get from QUADV with what you get if you did it using TRAPZ

f = @(x) exp(x.^2).*quad(@(z) exp(z.^2),-2,x);
trapz(arrayfun(f,-2:.001:2)) * 0.001
quadv(f,-2,2)

Both answers are very similar, about 541.38.

Best Answer

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MATLAB: Need help in evaluating integral with quad

MATLAB: Problem with integrals

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