LA_STEVR computes selected eigenvalues and, optionally,
the corresponding eigenvectors
of a real symmetric tridiagonal matrix 
. Eigenvalues
and eigenvectors can be selected by specifying either a range of
values or a range of indices for the desired eigenvalues.
LA_STEVR uses a relatively robust representation (RRR)
algorithm. It is usually the fastest algorithm of all
and uses the least workspace.