Looks for two consecutive small subdiagonal elements.
call pslaconsb(a, desca, i, l, m, h44, h33, h43h34, buf, lwork)
call pdlaconsb(a, desca, i, l, m, h44, h33, h43h34, buf, lwork)
The p?laconsb routine looks for two consecutive small subdiagonal elements by analyzing the effect of starting a double shift QR iteration given by h44, h33, and h43h34 to see if this process makes a subdiagonal negligible.
(global). REAL for pslaconsb
DOUBLE PRECISION for pdlaconsb
Array, DIMENSION (desca (lld_),*). On entry, the Hessenberg matrix whose tridiagonal part is being scanned. Unchanged on exit.
(global and local) INTEGER.
Array of DIMENSION (dlen_). The array descriptor for the distributed matrix A.
(global) INTEGER.
The global location of the bottom of the unreduced submatrix of A. Unchanged on exit.
(global) INTEGER.
The global location of the top of the unreduced submatrix of A. Unchanged on exit.
(global). REAL for pslaconsb
DOUBLE PRECISION for pdlaconsb
These three values are for the double shift QR iteration.
(global) INTEGER.
This must be at least 7*ceil(ceil( (i-l)/hbl )/lcm(nprow, npcol)). Here lcm is least common multiple and nprow*npcol is the logical grid size.
(global). On exit, this yields the starting location of the QR double shift. This will satisfy:
l ≤ m ≤ i-2.
(local).
REAL for pslaconsb
DOUBLE PRECISION for pdlaconsb
Array of size lwork.
(global). On exit, lwork is the size of the work buffer.