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 Author Comment/Response matteo 02/22/13 10:26am I am calculating eigenvalues of a set of M matrices which depend on a set of parameters (omegac, delta, G, J; G, J are left unspecified till the end) defined by: M = 11; omegac = 10; HA = SparseArray[{Band[{1, 1}] -> omegac, Band[{2, 1}] -> -J, Band[{1, 2}] -> -J}, {M, M}]; delta = 0; omegaq = delta + omegac; HAqn = Table[PadRight[HA, {M + n, M + n}], {n, 1, M}]; Do[HAqn[[j, M + n, M + n]] = omegaq, {j, 1, M}, {n, 1, j}]; Do[HAqn[[j, n, M + n]] = G, {j, 1, M}, {n, 1, j}]; Do[HAqn[[j, M + n, n]] = G, {j, 1, M}, {n, 1, j}]; EnAqn = Table[Eigenvalues[HAqn1[[n]]], {n, 1, M}]; The first M diagonal elements are omegac; the second M elements are omegaq. the matrix HAqn[[1]] has dimensions M+1, M+1; the HAqn[[2]] has dimensions M+2, M+2 etc. i would like to calculate the eigenvalues of these M matrices as a function of the parameter J for fixed parameter G, for example G=1. i then write: Plot[EnAqn[[1]], {t, 0, 2}, PlotRange -> {-3, 3}, AxesLabel -> {J/g, (\[Omega] - Subscript[\[Omega], c])/g}, AxesOrigin -> {0, -3}] for the eigenvalues of HAqn[[1]] and so on. the thing is i get wrong results!!!!! i really do not understand why. if i substitute a value of J already in the matrices and then calculate the eigenvalues the results are correct!! so i don't understand why assigning the value afterwards is wrong, as if the calculation of the eigenvalues with unspecified parameters would be wrong. any help would be great!!! Many many thanks!!!!!!!!!!! URL: ,
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