Developer Reference

  • 2020.2
  • 07/15/2020
  • Public Content
Contents

p?gehrd

Reduces a general matrix to upper Hessenberg form.

Syntax

call psgehrd
(
n
,
ilo
,
ihi
,
a
,
ia
,
ja
,
desca
,
tau
,
work
,
lwork
,
info
)
call pdgehrd
(
n
,
ilo
,
ihi
,
a
,
ia
,
ja
,
desca
,
tau
,
work
,
lwork
,
info
)
call pcgehrd
(
n
,
ilo
,
ihi
,
a
,
ia
,
ja
,
desca
,
tau
,
work
,
lwork
,
info
)
call pzgehrd
(
n
,
ilo
,
ihi
,
a
,
ia
,
ja
,
desca
,
tau
,
work
,
lwork
,
info
)
Include Files
Description
The
p?gehrd
routine
reduces a real/complex general distributed matrix sub(
A
) to upper Hessenberg form
H
by an orthogonal or unitary similarity transformation
Q'
*sub(
A
)*
Q
=
H
,
where sub(
A
) =
A
(
ia
:
ia
+
n
-1,
ja
:
ja
+
n
-1).
Input Parameters
n
(global)
INTEGER
. The order of the distributed matrix sub(
A
)
(
n
0)
.
ilo
,
ihi
(global)
INTEGER
.
It is assumed that sub(
A
) is already upper triangular in rows
ia
:
ia
+
ilo
-2
and
ia
+
ihi
:
ia
+
n
-1
and columns
ja
:
ja
+
ilo
-2
and
ja
+
ihi
:
ja
+
n
-1
. (See
Application Notes
below).
If
n
> 0, 1≤
ilo
ihi
n
; otherwise set
ilo
= 1,
ihi
=
n
.
a
(local)
REAL
for
psgehrd
DOUBLE PRECISION
for
pdgehrd
COMPLEX
for
pcgehrd
DOUBLE COMPLEX
for
pzgehrd
.
Pointer into the local memory to an array of size
(
lld_a
,
LOCc
(
ja
+
n
-1))
. On entry, this array contains the local pieces of the
n
-by-
n
general distributed matrix sub(
A
) to be reduced.