Derived Function Handle does not support integration operation, frustrating!

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Richard 2017-7-12

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编辑： Richard 2017-7-14

Try this piece of code, which works fine.

a=1;b=2;
% A two-variate function 
f2= @(x,y) x+y;
derivedF2=@(x) integral(@(y) f2(x,y), a,b);
% Test the evaluation of the derived function handle
derivedF2(0);
% Test the integration of the derived function handle
% integralVal=integral(derivedF2,a,b);
% integralVal=integral(@(x) derivedF2(x),a,b);
% Test plotting of the derived function handle
figure(11);
ezplot(@(x) arrayfun(derivedF2,x));

But if you uncomment the lines starting with integralVal. The code breaks.

Apparently, the derived function handle does not support integration operation, or have I missed something?

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Walter Roberson 2017-7-12

You have not defined a or b, so the code will not run.

Richard 2017-7-14

Sorry, I should have tested it before I posted.

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Answer 1

Steven Lord 2017-7-12

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在 MATLAB Online 中打开

When I ran this line of code (with the typo corrected, using derivedF2 instead of derivedF):

integralVal=integral(derivedF,a,b);

the error message I received said the following. I manually broke the message across two lines, so you don't need to scroll to read the whole thing.

 Error using integralCalc/finalInputChecks (line 515)
 Output of the function must be the same size as the input. If FUN is an
 array-valued integrand, set the 'ArrayValued' option to true.

When I did that:

>> integralVal=integral(derivedF2,a,b, 'ArrayValued', true)
integralVal =
     3

I used a = 1, b = 2.

I also recommend checking if integral2 will do what you need rather than calling integral twice.

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Richard 2017-7-14

Thanks! Yeah, the integral2 works fine. Thank you very much for your answer!

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Answer 2

Walter Roberson 2017-7-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/348471-derived-function-handle-does-not-support-integration-operation-frustrating#answer_273933

在 MATLAB Online 中打开

integralVal = integral(derivedF2, a, b, 'ArrayValued', true);

Or

integralVal = integral( @(X) arrayfun(derivedF2, X), a, b);

The basic problem is that integral() passes a vector as the first argument and the objective function must return a value for each member of the vector, and that happens at both levels when you have a nested integral() call.