MATLAB: Doesn’t calculate the integral (only int sign is added)

integral

I have difficulty in obtaining the indefinite integral equation.

Syms x

fun=x*sqrt(1+(1/9)*(1/x^(4/3)))

When I do int (fun, x), he just puts an integral sign in front of him. It does not provide the solution.

Best Answer

Actually, Wolfram Alpha got this one with no help. But sometime you need to do a little extra. The obvious thing I would try is a simple transformation. And the logical one is?

u = x^(1/3)

Or, if you prefer,

x = u^3

Then we have

dx = 3*u^2 du

The problem now reduces to:

Iu = int(u^3 * 3*u^2 * sqrt(1 + 1/9*u^(-4)),u)
Iu =
(u^2*(9*u^4 + 1)*(1/(9*u^4) + 1)^(1/2))/18

Now we can transform back to x using subs. Assuming my pencil and paper substitutions were correct.

Related Solutions

MATLAB: How to do numerical multiple integral (more than triple) by using matlab

You can use INT if your problem can be handled symbolically. If not, numerical integration of a 5-fold integral in MATLAB requires nesting INTEGRAL, INTEGRAL2, and INTEGRAL3. I got tired of explaining how to do this, so I wrote integralN and put it on the file exchange.

http://www.mathworks.com/matlabcentral/fileexchange/47919-integraln-m

There are some examples in the text at the top of the file. Basically, it's a straightforward extension of INTEGRAL2 and INTEGRAL3 in terms of how you call it.

You're going to have to reorder your variables because of the way your region is defined. By convention, the outermost integral is the first variable, and the innermost integral is the last. You need that reversed.

q = integeralN(@(e,d,c,b,a)fun(a,b,c,d,e),0,inf,0,@(e)e,0,@(e,d)d,0,@(e,d,c)c,0,@(e,d,c,b)b)

MATLAB: How to do integration using MATLAB

instead of using symbolic math you can use numerical integration .

function answer=myfunction(T)
   %* Labatto quadrature –
    q =quadl('(u.^4.*exp(u))./((exp(u)-1).^2)',0, T)
   %you can use quad() and trapz() functions instead
  end

Best Answer

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MATLAB: How to do numerical multiple integral (more than triple) by using matlab

MATLAB: How to do integration using MATLAB

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