Re: [Help-gsl] Can you do this in GSL?

[Kenneth Geisshirt]

Anders Misfeldt wrote:

> I wrote the integral wrong. Sorry! The correct function is:
>
> 0.067*b^3 = \int_0^b x^2/(exp(x)+1) dx

Assume that F(b) = \int_0^b x^2/(exp(x)+1) dx. Your equation is then 
0.067*b^3 = F(b) - F(0) = F(b). Now differentiate wrt b, and you have 
0.2*b^2 = F'(b) = f(b).

You can calculate f(b) as a finite difference, f(b) = 
(F(b+h)-F(b-h))/2h. In general you can calculate F(b) using an 
integration function found in GSL. Last, your solve the equation G(b) = 
f(b)-0.2*b^2 = 0 using a nonlinear equation solver in GSL.


--
Kenneth Geisshirt, M.Sc., Ph.D.   --   http://kenneth.geisshirt.dk/
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