Thread Subject: spline curve length

Hi

I want to estimate the length of a spline curve, I want to put this length in fmincon rutine as an object function. This is how I try
%%%%
C=spmak(knot, d');
fnplt(C)
Cprim=fnder(C);

ff=fnval(Cprim, param);
norma=((ff(1,:)).^2+ff(2,:).^2);
length=trapz(norma);
%%%%

but I'm not shure that this is it, because I get very big result. Is there any function in MATLAB whit which I can get spline curve length?

Thanks

"Didi Cvet" <didi_cvet@yahoo.com> wrote in message <h5rf05$nce$1@fred.mathworks.com>...
> Hi
>
> I want to estimate the length of a spline curve, I want to put this length in fmincon rutine as an object function. This is how I try
> %%%%
> C=spmak(knot, d');
> fnplt(C)
> Cprim=fnder(C);
>
> ff=fnval(Cprim, param);
> norma=((ff(1,:)).^2+ff(2,:).^2);
> length=trapz(norma);
> %%%%
>

I can't check your code carefully, but missing a square-root is what I have noticed.

Bruno

"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <h5rfog$btl$1@fred.mathworks.com>...
> "Didi Cvet" <didi_cvet@yahoo.com> wrote in message <h5rf05$nce$1@fred.mathworks.com>...
> > Hi
> >
> > I want to estimate the length of a spline curve, I want to put this length in fmincon rutine as an object function. This is how I try
> > %%%%
> > C=spmak(knot, d');
> > fnplt(C)
> > Cprim=fnder(C);
> >
> > ff=fnval(Cprim, param);
> > norma=((ff(1,:)).^2+ff(2,:).^2);
> > length=trapz(norma);
> > %%%%
> >
>
> I can't check your code carefully, but missing a square-root is what I have noticed.
>
> Bruno


I dont have square-root because my object function works with squared norm, however this doesn't solve my problem

Thanks anyway
Regards

  

"Didi Cvet" <didi_cvet@yahoo.com> wrote in message <h5rmcb$g64$1@fred.mathworks.com>...
>
> I dont have square-root because my object function works with squared norm, however this doesn't solve my problem
>

Then you are *not* interested in the *length* contrary to the subject line of the thread. Distance is integral of speed, not the square of speed.

Bruno

"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <h5rnpc$ht6$1@fred.mathworks.com>...
> "Didi Cvet" <didi_cvet@yahoo.com> wrote in message <h5rmcb$g64$1@fred.mathworks.com>...
> >
> > I dont have square-root because my object function works with squared norm, however this doesn't solve my problem
> >
>
> Then you are *not* interested in the *length* contrary to the subject line of the thread. Distance is integral of speed, not the square of speed.
>
> Bruno

I guess you are right, my problem is not in my object function then in the way I use fmincon because after this routine is called I get big estimate for the length (with sqrt in the formula), but that's another subject.

Sorry for badger and thank you for you time!

Greeting