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Topic: defining an unknown function
Replies: 1   Last Post: Jan 14, 2013 11:28 PM

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 Alexei Boulbitch Posts: 483 Registered: 2/28/08
Re: defining an unknown function
Posted: Jan 14, 2013 11:28 PM

Hi all,
I would like to start by defining H = {{\partial_{x,x} L,\partial_{x,y} L},
{\partial_{y,x} L, \partial_{y,y}L}};
where at this stage, the only think i know is that L is of the form L(x,y). This is a Hessian, and I would like to symbolically compute the e-vals and e-vecs. I wanted to know how I should tell mathematica to consider L as L(x,y) ?

Thanks,
Sid.

Hi, Sid,

Is this:

H[f_]:=Det[{{D[f,{x,2}],D[D[f,x],y]},{D[D[f,y],x],D[f,{y,2}]}}]//Simplify;

H[Sin[x*y]]

Cos[x y] (-Cos[x y]+2 x y Sin[x y])

the function that you mean?

Have fun, Alexei

Alexei BOULBITCH, Dr., habil.
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Date Subject Author
1/11/13 siddys@gmail.com
1/14/13 Alexei Boulbitch