Re: definite numerical integration

[David Bateman]

roberto wrote:

> hello,
> i need some hint about the following topic:
>
> 1. take a function f(r; a), where "a" is a parameter, whose analytical
> form i don't know explictly but i can evaluate it point by point in a
> given interval [0,r_max]
> (i already wrote Octave code for this);
>
> 2. i have to evaluate the definite integral of f(r; a) in [0,r*]
> (where r*<r_max);
>
> 3. doing this, evaluating the integral by varying r* in [0,R] (e.g. R = 110)
> i'll have a function F(r*,a) where a should be obtained by imposing
> some boundary condition;
>
> i looked for some help into Octave like 
> http://octave.sourceforge.net/index/Q.html
>
> but in libraries like:
> [v, ier, nfun, err] = quad (f, a, b, tol, sing) 
>
> the function to be integrated are to be inserted by their explicit formulation
> which i don't have now, as already stated above;
>
>  
I don't quite see the problem as in 1) you saw you have a function to 
numerically calculate the values in a range [0,r_max] and then in 3) you 
state you can use a explicit formulation

What about something like

function y = fun (x)
 # Nasty integrable singularity to be unkind to quad and show octave's 
better here :-)
 y  = 1/x;
endfunction

[v, ier, nfun, err] = quad (@fun, 1, 3, 1e-6)

I was going to integrate over the range [-1:1] above, but that seems to 
seg-fault in dqpsrt.f.
Looking at it...

Cheers
David




> thank you very much for any help about this topic, since it's the last
> step of my work up to now
> bye
>  


--
David Bateman                                address@hidden
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
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