Re: Eigenvalues works very slow
- To: mathgroup at smc.vnet.net
- Subject: [mg128495] Re: Eigenvalues works very slow
- From: "Harker, Anthony" <a.harker at ucl.ac.uk>
- Date: Thu, 25 Oct 2012 01:41:53 -0400 (EDT)
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As you want real values in the end, stop Mathematica from manipulating enormously complicated exact expressions by letting Eigenvalues[] work on the real form: Eigenvalues[N[q4 + h0]] Tony Harker ]-> -----Original Message----- ]-> From: jure lapajne [mailto:lapajne.jure at gmail.com] ]-> Sent: 24 October 2012 08:30 ]-> To: mathgroup at smc.vnet.net ]-> Subject: Eigenvalues works very slow ]-> ]-> 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. ]->
- References:
- Eigenvalues works very slow
- From: jure lapajne <lapajne.jure@gmail.com>
- Eigenvalues works very slow