This subroutine forms the eigenvectors of a complex Hermitian matrix
by back transforming those of the corresponding real symmetric tridiagonal
matrixdetermined by htridi.
ar[1..n,1..n] and ai[1..n,1..n] contain information about the unitary
transformations used in the reduction by htridi in their full lower
triangles except for the diagonal of ar.
tau[1..2,1..n] contains further information about the transformations.
m is the number of eigenvectors to be back transformed.
zr contains the eigenvectors to be back transformed in its first
m columns (from tqli or tql2).
zr[1..n,1..n] and zi[1..n,1..n] contain the real and imaginary parts,
respectively, of the transformed eigenvectors in their first m columns.
Note that the last component of each returned vector is real
and that vector euclidean norms are preserved.
( see the original EISPACK comment for htribk in implementation ).
pascal variant by Nikolai V. Shokhirev 2002