Developer Reference

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

?trtri

Computes the inverse of a triangular matrix.

Syntax

call strtri
(
uplo
,
diag
,
n
,
a
,
lda
,
info
)
call dtrtri
(
uplo
,
diag
,
n
,
a
,
lda
,
info
)
call ctrtri
(
uplo
,
diag
,
n
,
a
,
lda
,
info
)
call ztrtri
(
uplo
,
diag
,
n
,
a
,
lda
,
info
)
call trtri
(
a
[
,
uplo
]
[
,
diag
]
[
,
info
]
)
Include Files
  • mkl.fi
    ,
    lapack.f90
Description
The routine computes the inverse
inv(
A
)
of a triangular matrix
A
.
Input Parameters
uplo
CHARACTER*1
.
Must be
'U'
or
'L'
.
Indicates whether
A
is upper or lower triangular:
If
uplo
=
'U'
, then
A
is upper triangular.
If
uplo
=
'L'
, then
A
is lower triangular.
diag
CHARACTER*1
.
Must be
'N'
or
'U'
.
If
diag
=
'N'
, then
A
is not a unit triangular matrix.
If
diag
=
'U'
,
A
is unit triangular: diagonal elements of
A
are assumed to be 1 and not referenced in the array
a
.
n
INTEGER
.
The order of the matrix
A
;
n
0
.
a
REAL
for
strtri
DOUBLE PRECISION
for
dtrtri
COMPLEX
for
ctrtri
DOUBLE COMPLEX
for
ztrtri
.
Array:
size
lda
by *
size max(1,
lda
*
n
)
. Contains the matrix
A
.
The second dimension of
a
must be at least
max(1,
n
)
.
lda
INTEGER
.
The first dimension of
a
;
lda
max(1,
n
)
.
Output Parameters
a
Overwritten by the matrix
inv(
A
)
.
info
INTEGER
.
If
info
= 0
, the execution is successful.
If
info
=
-i
, the
i
-th parameter had an illegal value.
If
info
=
i
, the
i
-th diagonal element of
A
is zero,
A
is singular, and the inversion could not be completed.
LAPACK 95 Interface Notes
Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see LAPACK 95 Interface Conventions.
Specific details for the routine
trtri
interface are as follows:
a
Holds the matrix
A
of size (
n
,
n
).
uplo