Why receive error Integrand output size does not match the input size?

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Mehdi 2023-1-20

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https://ww2.mathworks.cn/matlabcentral/answers/1897595-why-receive-error-integrand-output-size-does-not-match-the-input-size

评论： Mehdi 2023-1-22

采纳的回答： Torsten

在 MATLAB Online 中打开

Where is the problem?

clear
syms x y
f=0*x*y;
Hf = matlabFunction(f,'Vars',[x y])
Hf = function_handle with value:
    @(x,y)0.0
integral2(Hf,-1,1,-1,1);
Error using integral2Calc>integral2t/tensor
Integrand output size does not match the input size.

Error in integral2Calc>integral2t (line 55)
[Qsub,esub] = tensor(thetaL,thetaR,phiB,phiT);

Error in integral2Calc (line 9)
    [q,errbnd] = integral2t(fun,xmin,xmax,ymin,ymax,optionstruct);

Error in integral2 (line 105)
    Q = integral2Calc(fun,xmin,xmax,yminfun,ymaxfun,opstruct);

采纳的回答

Torsten 2023-1-20

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编辑：Torsten 2023-1-20

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x and y that are inputs to Hf from integral2 are usually matrices (of the same size).

The output of Hf is expected to be of the same size as x (or y).

Thus if you only return 0 (a scalar value which is usually not of the same size as x (or y)), you get an error message.

Since I saw the typical functions you want to integrate are that complicated that this problem would never occur, I didn't include this simple case in my answer.

But if you want to cover the special case of a constant function, too, use

syms x y
f=0*x*y;
Hf = matlabFunction(f,'Vars',[x y])
Hf = function_handle with value:
    @(x,y)0.0
Hf = @(x,y)Hf(x,y).*ones(size(x))
Hf = function_handle with value:
    @(x,y)Hf(x,y).*ones(size(x))
integral2(Hf,-1,1,-1,1)
ans = 0

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Torsten 2023-1-20

编辑：Torsten 2023-1-20

@Mehdi

I wonder why you go into these specialities and make things so complicated.

If you want to apply integral2 to each component of a vector-values function, use a (parfor) loop over its components.

Mehdi 2023-1-20

I used a (parfor) loop over its components, but receved error when the components are zero valued.

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Walter Roberson 2023-1-20

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If you have f, a symbolic expression nominally in x and y, but which might in practice turn out to be independent of both x and y and so matlabFunction() will not vectorize, then you have three options.

First, you can do what @Torsten showed, of multiplying the output by ones() to do implicit expansion.

Second, you can use

Hf = matlabFunction(f,'Vars',[x y]);
wrapper = @(X,Y) arrayfun(Hf, X, Y);
result = integral2(wrapper, -1, 1, -1, 1);

Third, you can use

xlow = -1; xhigh = 1;
ylow = -1; yhigh = 1;
if isempty(symvar(f))
    result = double(f) .* (xhigh - xlow) .* (yhigh - ylow);
else
    Hf = matlabFunction(f, 'vars', [x, y]);
    result = integral2(Hf, xlow, xhigh, ylow, yhigh);
end

as there is no need to call an integration function for a result so simple.

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Walter Roberson 2023-1-22

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Do not use syms within a parfor loop. syms is not a "keyword", it is a MATLAB function, and it creates variables by using assignin('caller'), not through MATLAB having any special knowledge. That is a problem in parfor because parfor needs to see clearly where variables are created, but parfor does not know that syms creates variables.

ali()
function kdl = ali()
x = sym('x');
y = sym('y');
H=[0*x*y;0*x;0*y;0;x*y];
 parfor i=1:length(H)
    Hf = matlabFunction(H(i), 'Vars' ,[x y]);
    wrapper = @(x,y) arrayfun(Hf, x, y);
    kdl(i)= integral2(wrapper,-1,1,-1,1);
 end
end