Not enough input arguments in trapz

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Andrei
Andrei 2023-7-2
回答： John D'Errico 2023-7-2
I am currently trying to perfor, numerical integration inb polar coordinates. I used trapz function this way:
Nx = 402;
x = linspace(-L/2,L/2, Nx);
y = linspace(-L/2, L/2, Ny);
[X,Y] = meshgrid(x(2:end-1), y(2:end-1));
[TH,R] = cart2pol(X,Y);
alpha_1 = linspace(0, pi/5, Nx-2);
ro = linspace(0, 20, Nx-2);
P_1 = trapz(alpha_1, (trapz(ro, (abs(v).*R), 2)),1);
v is a complex valued (400,400) matrix with non zero elements. I wanted to find volume under this function within angle pi/5 (special region in my task). But I came across an error: Not enough input arguments in line with trapz(). Where is the mistale, I checked documentation, everything should be fine. I tried to remove dim = 1 in outer integral - got same error.
  1 个评论
Catalytic
Catalytic 2023-7-2
编辑：Catalytic 2023-7-2
Ran in:
Please provide code that can demonstrate the error and then run it for us like I've done below. As you can see, when I run your code with fabricated values, I get a value for P_1 with no error messages.
Nx = 402;Ny=402; v=rand(400); L=100;
x = linspace(-L/2,L/2, Nx);
y = linspace(-L/2, L/2, Ny);
[X,Y] = meshgrid(x(2:end-1), y(2:end-1));
[TH,R] = cart2pol(X,Y);
alpha_1 = linspace(0, pi/5, Nx-2);
ro = linspace(0, 20, Nx-2);
P_1 = trapz(alpha_1, (trapz(ro, (abs(v).*R), 2)),1)
P_1 = 239.0549

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John D'Errico
John D'Errico 2023-7-2
I would strongly suggest you should not name your own functions the same as existing code. If you do, then this is exactly the type of error you should expect. To learn if what I suspect is true, do this at the command line.
which trapz -all
It should show a function named trapz that you wrote. If so, then rename your function.

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