Hi,
For your information: For some matrices DSYEVR, when told to compute a
small number of eigenvalues, returns nonorthogonal eigenvectors.
Perhaps it possible for the algorithm to detect this and return with an
error?
This applies at least when using the automatically chosen ABSTOL.
However, at least for the example below, I wasn't able to find a
suitable ABSTOL for which it would work.
Maybe, this might have to do with the fact that for the example problem
below, the first eigenvalue is multiply degenerate, and the numerical
second eigenvalue is epsclose to the first one.
The following test program illustrates this:
http://projects.scipy.org/scipy/rawattachment/ticket/1159/test.f90
with the test data
http://projects.scipy.org/scipy/rawattachment/ticket/1159/L.txt
On Lapack 3.2.1 + reference BLAS, I get:
$ gfortran o test test.f90 llapack lblas
$ ./test < L.txt
orth error ( 2 eigs): 0.96599125529927221 HUGE ERROR
orth error ( 3 eigs): 0.96599125529927232 HUGE ERROR
orth error ( 4 eigs): 0.96599125529927221 HUGE ERROR
orth error ( 5 eigs): 2.52928802610462387E017
orth error ( 6 eigs): 1.47893223140021721E016
orth error ( 7 eigs): 1.18177613284446356E016
orth error ( 8 eigs): 0.0000000000000000
orth error ( 9 eigs): 2.84549495443531079E016
orth error ( 10 eigs): 2.93456682158620488E016
