INT will not evalaute integral

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I have a code that needs to evalaute the arc length equation below:

syms x
a = 10;
b = 10;
c = 10;
d = 10;
fun = 4*a*x^3+3*b*x^2+2*c*x+d
int((1+(fun)^2)^.5)

but all that returns is below:

ans =

int(((40*x^3 + 30*x^2 + 20*x + 10)^2 + 1)^(1/2), x)

Why wont matlab evaluate this integral? I added a line under to check if it would evaulate int(x) and it returned the desired result.

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Answer 1

Mischa Kim 2014-6-30

编辑：Mischa Kim 2014-6-30

在 MATLAB Online 中打开

1 个投票

Dan, try instead

int((1+fun^2)^5,x)

or

vpa(int((1+fun^2)^5,x),4)

for better readability.

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Dan Kenney 2014-6-30

I copied and pasted that code and it evaluated the integral, but I realized it was raised to 5, not (1/2). Is there such a thing as too complicated an integral for matalb? I figured this was not that difficult of an operation to perform.

Mischa Kim 2014-6-30

Well, there is probably no closed-form solution, which is why MATLAB's Symbolic Math Toolbox won't do the trick. In this case, use numeric integration.

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