# Re: [theano-users] derivative of function based on eigenvalues in theano

```The problem is smat(x)

It return list of list of Theano variable. This isn't a Theano variable
itself. You can have Theano contact all of this correctly to make a new
corresponding Theano variable with:```
```
v,w=nlin.eigh(theano.tensor.stacklists(smat(x)))

Fred

On Tue, Aug 1, 2017 at 7:37 AM Jyotiranjan Beuria <
jyotiranjan.beu...@gmail.com> wrote:

> Hi All,
>
> I am trying to calculate the derivative of a function that
> depends on eigenvalues of a matrix. I am new to Theano.
> Here is a snippet of the code.
> import numpy as np
>
> import theano
> import theano.tensor as T
> import theano.tensor.nlinalg as nlin
>
> def myFun(X,a=2):
>     s=T.dmatrix('s')
>     x=T.dvector('x')
>     a=T.dscalar('a')
>     def smat(x):
>       return  [[x[0]**2,x[1],x[2]],
>                [x[1]**2,a*x[1],a*X[0]],
>                [x[2]**2,x[0],a*x[1]]]
>     v,w=nlin.eigh(smat(x))
>     Eigen,Grad = theano.function([x], [v,TG],allow_input_downcast=True )
>
>     ev=Eigen(X)
>     print ev,der
>
> myFun([2,3,5])
>
> Can anyone help me to solve this problem?
>
> Regards,
> Jyotiranjan
>
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