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Re: defining an unknown function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg129451] Re: defining an unknown function
  • From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
  • Date: Mon, 14 Jan 2013 23:30:45 -0500 (EST)
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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.
IEE S.A.
ZAE Weiergewan,
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e-mail: alexei.boulbitch at iee.lu<mailto:alexei.boulbitch at iee.lu>



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