what's the difference between dsyev/x/r/d?

[bsmile]

and what are their performance difference?

Thanks,

[admin]

Here is the difference:
- eigenvalues only: SYEV
- eigenvectors and eigenvalues:
* subset computation: SYEVR or SYEVX
* all eigenvectors: SYEVD or SYEVR or SYEVX

Which one is faster depends on the matrices.

See, for example:
http://www.netlib.org/lapack/lawnspdf/lawn182.pdf