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## Re: [Help-gsl] How to Fit an intracable formula

**From**: |
Alex Brussee |

**Subject**: |
Re: [Help-gsl] How to Fit an intracable formula |

**Date**: |
Tue, 13 Jul 2004 10:40:14 +0100 |

Hi Brian Gough,

`Thank you for helping me out. A little time ago I sent a question like this,
``and you gave me the advice to look at gls_multimin_fdf, which i did. That
``worked for me, I now have a solution that seems to work.
`

`For other people who are trying to find a gradient, this is my code for the
``derivative
`
void FDF(const gsl_vector *Vec, void *Param, gsl_vector *dVec)
{
double *P = (double *)Param;
gsl_multimin_function FMF ;// this part was very helpful, thx Brian !
FMF.f = F;
FMF.params = P;
FMF.n = Vec->size;
gsl_multimin_diff (&FMF, Vec, dVec);
}

`By the way, my formula has to be calculated numerically, beceause the
``"simple" formula from my previous mail was the speed for the left and right
``wheel of my robot, and with these speeds a formula can be set up for
``differential driving. After this, the resulting robot position is
``intracable.
`I mixed up x(t) with v(t):
vr(t)=Amp1*((1/(tau1-tau2))*exp(t/tau1)-(1/(tau1-tau2))*exp(t/tau2))
vl(t)=Amp2*((1/(tau3-tau4))*exp(t/tau3)-(1/(tau3-tau4))*exp(t/tau4))
Fill this in in:
x(t)=x0+b(vr+vl)/(vr-vl)*(sin((vr-vl)t/b+phi0)+sin(phi0))
y(t)=y0-b(vr+vl)/(vr-vl)*(cos((vr-vl)t/b+phi0)-cos(phi0))

`And the resulting points X(t), Y(t) need to be fitted on a Minimal Jerk 5th
``Order Spline.
`
Sorry to bother you, and thx for the help !
Alex Brussee
:)
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