# [SciPy-user] Another leastsq Jacobian bug

Lin Shao shao@msg.ucsf....
Tue Jun 26 11:47:43 CDT 2007

```No I didn't. The simplest refute to your answer is that your J[1] is
-2*params[0]*(xx*params[1]-params[1]^2). How could there be a term
with params[1]'s quadratic in the derivative if the original function
is a quadratic function?

On 6/25/07, Christian K <ckkart@hoc.net> wrote:
> Lin Shao wrote:
> >>> ## Now define my Jacobian
> >>> def Jacobian(params,xx,yy,mode='col'):
> >>>     J = N.empty((len(params),xx.size))
> >>>     J[0] = (xx-params[1])**2
> >>>     J[1] = -2*params[0]*(xx-params[1])
> >> shouldn't that be -2*params[0]*(xx-params[1])*params[1]  ?
> >
> > I think I was right. Think about what's the derivative of -x^2 -- it's -2x
>
> you forgot about the chain rule .
>
> Christian
>
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>
```

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