How to get results from symbolic variable integration

Question

Hosup Song 2016-7-27

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https://ww2.mathworks.cn/matlabcentral/answers/297422-how-to-get-results-from-symbolic-variable-integration

评论： Walter Roberson 2016-7-28

采纳的回答： Walter Roberson

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Pretty straight forward, I'm trying to do integration with symbolic variables.

I'm doing some complex integration with a mix of high degree polynomials and trig functions.

This is what I tried so far:

syms x
b4 = (x^127+x^32-x^12+78*x^2-5*cos(x))
int(b4, 0, 1)

I was hoping to get some number for the answer, but instead, I got this:

ans =
int((x^127+x^32-x^12+78*x^2-5*cos(x)), x, 0, 1)

I don't know why this is happening. How do I get the actual answer in numbers?

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Answer 1

Walter Roberson 2016-7-27

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There is no readily-found closed-form solution for your actual integral. You will need to use vpa() or double() to request numeric integration.

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Hosup Song 2016-7-28

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so would i have to do something like

b4 = (((1+x^3+x^i)^(1/2))*((1/0.00149912)*(cos(x)-30*(6-11*sin(1)+...
      6*cos(1))*x^2+(192-336*sin(1)+168*cos(1))*x-36+57*sin(1)-24*cos(1))))
A = int(b4, 0, 1)
double(A)

Would this give me a numeral value for the answer?

Walter Roberson 2016-7-28

Yes, it would give you a numeric value for the integral.

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Answer 2

Andrei Bobrov 2016-7-27

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https://ww2.mathworks.cn/matlabcentral/answers/297422-how-to-get-results-from-symbolic-variable-integration#answer_229982

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in R2016a

>> syms x
b4 = (x^127+x^32-x^12+78*x^2-5*cos(x));
int(b4, 0, 1)
ans =
1425581/54912 - 5*sin(1)
>>

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Hosup Song 2016-7-27

编辑：Walter Roberson 2016-7-27

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ok i guess that was a bad example to use, since it works out nicely. The actual function I'm using is

b4 = (((1+x^3+x^i)^(1/2))*((1/0.00149912)*(cos(x)-30*(6-11*sin(1)+...
        6*cos(1))*x^2+(192-336*sin(1)+168*cos(1))*x-36+57*sin(1)-24*cos(1))))

I'm trying to integrate this and when I use int(b4, 0, 1), i get ans =

int((x^3 + x^1i + 1)^(1/2)*((1885688952269973342506590723*x)/77371252455336267181195264 + (5867504283985271*cos(x))/8796093022208 + (1423673755532221964006035379175*x^2)/4951760157141521099596496896 - 1657186126350190416636264063127/2475880078570760549798248448), x, 0, 1)

How do i get rid of this.

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