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Eigenvalues works very slow

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128478] Eigenvalues works very slow
  • From: jure lapajne <lapajne.jure at gmail.com>
  • Date: Wed, 24 Oct 2012 03:30:27 -0400 (EDT)
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Hello,
I'm trying to calculate eigenvalues of different sized matrices (from 10x10 to 1000x1000) using mathematica's built-in function - Eigenvalues. For smaller matrices it works ok, but for larger matrices it's just too slow. I tried writing the code in another system and it finds eigenvalues very quickly (in a second or two at most) even for big matrices. I'm not sure whether am I doing something wrong or is the speed difference really this big.
My code (you only need to change d to change the size of matrix):
d = 25;
q = Table[Table[1/2*Sqrt[i + j + 1]*KroneckerDelta[Abs[i - j], 1], {j, 0, d-1}],{i, 0, d - 1}];
h0 = Table[Table[(i + 1/2)*KroneckerDelta[i, j], {j, 0, d - 1}], {i, 0,d-1}];
lambda = 1/2;
q4 = lambda*q.q.q.q;
N[Eigenvalues[q4 + h0]]

Thanks for help.



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