Integration is not as I expect

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Abdulaziz Abutunis 2015-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/195497-integration-is-not-as-i-expect

评论： Abdulaziz Abutunis 2015-4-1

Hi all, Please I have an integration I am trying to solve using matlab. The integration derived me crazy because i know the output and matlab does not give me the same answer.

my code is simple and as follow

syms U_0 x L v X
U=U_0*(1-(x/L));
y=((((0.45*v)/(U^6))*(int(U^5,x,0,x))))

The answer I got is

y= (3*v*x*(6*L^5 - 15*L^4*x + 20*L^3*x^2 - 15*L^2*x^3 + 6*L*x^4 - x^5))/(40*L^5*U_0*(x/L - 1)^6)

While the right answer I should receive is

y= (0.075*L*v*(1/(x/L - 1)^6 - 1))/U_0

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Answer 1

John D'Errico 2015-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/195497-integration-is-not-as-i-expect#answer_173483

And you are absolutely positive that the two forms are not mathematically equivalent? You have checked that carefully?

The thing about symbolic computations is the computer need not return a result that is in exactly the form you recognize. That need not make it wrong.

So why not look more carefully at that result? You might surprise yourself.

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Abdulaziz Abutunis 2015-3-31

Thank you John for your response. I just supstract the equations from each other and the results was not zero. I do not know if there is a way in matlab that turn equations in particular format. I try simplify no thing was changed. I will try to simplify it by hand. Thanks again

Abdulaziz Abutunis 2015-4-1