Re: What did I do wrong with this funtion? - Implementing msplines

[Corrado]

Dear Jaroslav,

thanks for your help. I prototyped using R originally, and then rewrote it in 
Octave. Two quick questions:

1) How can I make the function more efficient?
2) Do you think I should rather write it in Fortran or any other language, 
instead of Octave?

Regards

On Wednesday 16 September 2009 10:26:43 Jaroslav Hajek wrote:
> On Wed, Sep 16, 2009 at 10:10 AM, Corrado <address@hidden> wrote:
> > Dear friends,
> >
> > I am trying to implement in Octave the two spline families as in the
> > documentation here below attached. I am a newbie to Octave, and this is
> > my first function.
> >
> > I built the function:
> >
> > function retspline = mspline (i,x,k,t)
> >        # i is the spline index in the family
> >        # x is the variable
> >        # t is the vector of knots, t(h) is the h-th knot
> >        # k is the Mspline degree
> >
> >        I=i
> >
> >        if(k==1)
> >
> >                if(x<t(i+1) & x>=t(i))
> >                        td=t(i+1)-t(i)
> >                        M=1/td
> >                else
> >                        M=0
> >                endif
> >
> >        else
> >
> >                kk=(k-1)
> >
> >                if (x>=t(i) & x<t(i+k))
> >                        M=k*((x-t(i))*mspline(i=I,x=x,k=kk,t=t)+(t(i+k)-
> > x)*mspline(i=(I+1),x=x,k=kk,t=t))/((k-1)*(t(i+k)-t(i)))
> >                elseif (x<t(i) | x>=t(i+k))
> >                        M=0
> >                endif
> >
> >        endif
> >
> >        retspline=M
> >
> > endfunction
> >
> > but for some reason it does not work ....
> >
> > I add that I am a newbie with Octave, please do not shut me.
> >
> > What did I do wrong?
> >
> > Best,
> > --
> > Corrado Topi
>
> You're probably misinterpreting the expression
> `mspline(i=I,x=x,k=kk,t=t)'  (did you program in Python or Fortran?)
> In Octave, there is no passing parameters by name, and the expression
> is interpreted like in C, so that it means:
> i=I,x=x,k=kk,t=t,mspline(i,x,k,t)
> which probably spoils your script by overwriting variables. I didn't
> check for other problems.
> Note that even if you succeed, this will be a very inefficient
> implementation in Octave, but probably good enough to start
> programming.
>
> hth



-- 
Corrado Topi

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