[Octave-bug-tracker] [bug #60924] DNAUPD did not find any eigenvalues to sufficient accuracy

[Dmitri A. Sergatskov]

Follow-up Comment #6, bug #60924 (project octave):

I played a little more -- it looks like sometimes I do not get
warning. Not sure anymore if "clear" has an effect. 
With both openblas (OMP) and ref blas.


 LD_PRELOAD=/usr/lib64/libblas.so octave -q -f
octave:1> t1
error: eigs: error in dneupd: DNAUPD did not find any eigenvalues to
sufficient accuracy.
This should not happen.  Please, see
https://www.gnu.org/software/octave/bugs.html, and file a bug report
error: called from
    eigs at line 298 column 20
    t1 at line 20 column 9
octave:2> t1
octave:3> t1
error: eigs: error in dneupd: DNAUPD did not find any eigenvalues to
sufficient accuracy.
This should not happen.  Please, see
https://www.gnu.org/software/octave/bugs.html, and file a bug report
error: called from
    eigs at line 298 column 20
    t1 at line 20 column 9
octave:4> t1
error: eigs: error in dneupd: DNAUPD did not find any eigenvalues to
sufficient accuracy.
This should not happen.  Please, see
https://www.gnu.org/software/octave/bugs.html, and file a bug report
error: called from
    eigs at line 298 column 20
    t1 at line 20 column 9
octave:5> 



cat t1.m 
nplots = 50;
xmax = 200;
alpha = 4;
myeps = 6;
N = 2^10;
h = xmax/N;
x = h*(1:N)-xmax/2;
t = 0;
u = sech(sqrt(3*alpha/(4*myeps))*x).^2;
tdata = zeros(nplots+1,1);
tdata(1) = t;
num_eigs = 1;
eigenvalues = zeros(length(tdata),num_eigs);
N_eig = 2^10;
k_eig = [0:N_eig/2 -N_eig/2+1:-1]*(2*pi/(xmax/2));
ksq_eig = k_eig.^2';
u_eig = u';
A = @(f) real(-ifft( -(myeps/6)^(2/3)*ksq_eig .* fft(f)) -
alpha/(4*(myeps/6)^(1/3))*u_eig .* f);
[~,lam] = eigs(A,N_eig,num_eigs,'sr',struct('isreal',true));



Dmitri.
-- 



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