Error when using abs: Too many input arguments

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Sergio Manzetti
Sergio Manzetti 2021-6-22
评论： Dhruv G 2021-6-22
Hi, I am trying to plot the contour of the given function with the following:
syms r x y k z
[ph,r] = meshgrid((0:5:360)*pi/180,0:.5:10);
[X,Y] = pol2cart(ph,r);
Z = X+i*Y;
J = besselj(k,l.*r);
J2 = besselj(k,m.*r);
Y = bessely(k,l.*r);
Y2 = bessely(k,m.*r);
H = besselh(k,r);
F1 = symsum((J).*exp(1i*k*ph),k,-5,5);
F2 = symsum((J2+Y2).*exp(1i.*k.*ph),k,-5,5);
F3 = symsum(H.*exp(1i.*k.*ph),k,-5,5);
pwu = nan(size(F1), 'like', F1);
mask = 0 <= r & r < 0.5;
pwu(mask) = F1(mask);
mask = 0.5 <= r & r < 1;
pwu(mask) = F2(mask);
mask = r >= 1;
pwu(mask) = F3(mask);
U = subs(pwu, {l, m}, {1.5, 3});hold on
contour(X,Y,abs(double(U)),30)
axis equal
xlabel('r','FontSize',14);
ylabel('phi','FontSize',14);
But I get the error that there too many input arguments. If I remove "double" from the 4th last line, then it says input arguments must be numeric so to be converted to a double. So which way is correct here?
Thanks!

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回答（1 个）

Dhruv G
Dhruv G 2021-6-22
If you type 'U' in the command window you would find that it is an array of symbolic equations (or expressions I'm not too sure). I think this is happening due to the symsum in your code. This is why it's not possible to cast U into a double and why you're getting the error.
  2 个评论
Sergio Manzetti
Sergio Manzetti 2021-6-22
Thanks for this. Does it mean I cannot plot the contour of this function?
Dhruv G
Dhruv G 2021-6-22
I think if you replace symsum with a function that does what you want numerically it should be possible

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