Integration of MATLAB function - NOT Mathematic function.

Question

Echo-6 2016-9-2

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评论： Walter Roberson 2016-9-3

Hi, I have three MATLAB script, with one serve as a main class. I want to integrate an expression which contain two other functions,

Code:

x = 0:180;
TB = integral(getCt_Theta(x)*getQ_2(x),1,180);

Where: getCt_Theta(x), is a function to calculate coefficient of lift, will return one values for each inputs Same goes for getQ_2(x), The reason for this task is to evaluate half revolution of the turbine. Should I do symbolic first? or should I Simulink it?

Thanks everyone!

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Walter Roberson 2016-9-2

Your x is the integral values from 0 to 180, but you mention x in your integral() and you want the integral to be over 1 to 180. Is your x intended to be continuous or discrete, and is it intended to be 0 to 180 or 1 to 180 ?

Echo-6 2016-9-3

编辑：Echo-6 2016-9-3

Hi Walter, My bad, I intent to integrate from 0-180. The raw data one of the function access to is from a CSV file, interpolated. So it's continuous.

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Answer 1

Walter Roberson 2016-9-3

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在 MATLAB Online 中打开

f = @(x) getCt_Theta(x).*getQ_2(x)

and integral that:

integral(f, 0, 180)

However, this depends upon getCt_Theta and getQ_2 accepting vectors of values. If they cannot, if they can only accept scalars, then you need

integral( @(X) arrayfun( f, X), 0, 180)

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Echo-6 2016-9-3

Awesome man! Now I got the integration result! Thanks!

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Answer 2

Pawel Ladosz 2016-9-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/301733-integration-of-matlab-function-not-mathematic-function#answer_233638

在 MATLAB Online 中打开

You could try and change your matlab function to function handle by:

getCt_Theta_fun=@getCt_Theta

Then you can use this is as input to integral. However I am not sure whether it would deal with multiplication of the function handles.

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Echo-6 2016-9-3

编辑：Walter Roberson 2016-9-3

在 MATLAB Online 中打开

Dear Adam, I have try the function handle by using only getQ_2 first. Just to prove the concept. The function is valid from 0-180, I have check it.

Code I try

f = @(theta) getQ_2;
TB = integral(f,1,180);

I got the following error-

Not enough input arguments.
Error in getQ_2 (line 2)
theta= deg2rad(theta);
Error in Int_test_1>@(theta)getQ_2
Error in integralCalc/iterateScalarValued (line 314)
                fx = FUN(t);
Error in integralCalc/vadapt (line 132)
            [q,errbnd] = iterateScalarValued(u,tinterval,pathlen);
Error in integralCalc (line 75)
        [q,errbnd] = vadapt(@AtoBInvTransform,interval);
Error in integral (line 88)
Q = integralCalc(fun,a,b,opstruct);
Error in Int_test_1 (line 5)
TB = integral(f,1,180);