Using an integral in a function

Question

Yu Haobo Yu 2020-10-21

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/621073-using-an-integral-in-a-function

评论： Yu Haobo Yu 2020-10-21

采纳的回答： Stephen23

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Hi, I have a problem as follows:

In the main file, I define a function f_1 and a number q_Max:

q_Max=10;
f_1 = @(q) (0).*((q<0)|(q>q_Max)) + (q*height/peak_1).*((0<=q) & (q<=peak_1)) +...
    (height-(q-peak_1)*height/(q_Max-peak_1)).*((peak_1<q) & (q<=q_Max));

In a function file, I define the following function:

function result = Lambda_1(beta)
global f_1 q_Max
result = beta*integral(@(q) f_1(q).*q.^2,0,q_Max);
end

In the main file, I run the following line and get an error:

Lambda_1(0.1)
Error using integral (line 85)
A and B must be floating-point scalars.
Error in Lambda_1 (line 10)
result = beta*integral(@(q) f_1(q).*q.^2,0,q_Max);

I wonder why this happens. I think both q and q_Max are scalars. Thanks in advance.

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Answer 1

Stephen23 2020-10-21

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/621073-using-an-integral-in-a-function#answer_520068

The problem is that in the "main file" you did not declare q_Max and f_1 as global.

But rather than using global variables (which should be avoided) you would be much better of parameterizing the function using one of the recommended syntaxes:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html