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dtrtri.f
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*>
\
brief
\
b
DTRTRI
*
*
===========
DOCUMENTATION
===========
*
*
Online
html
documentation
available
at
*
http
:
//
www
.
netlib
.
org
/
lapack
/
explore
-
html
/
*
*>
\
htmlonly
*>
Download
DTRTRI
+
dependencies
*>
<
a
href
=
"http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dtrtri.f"
>
*>
[
TGZ
]
</
a
>
*>
<
a
href
=
"http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dtrtri.f"
>
*>
[
ZIP
]
</
a
>
*>
<
a
href
=
"http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dtrtri.f"
>
*>
[
TXT
]
</
a
>
*>
\
endhtmlonly
*
*
Definition
:
*
===========
*
*
SUBROUTINE
DTRTRI
(
UPLO
,
DIAG
,
N
,
A
,
LDA
,
INFO
)
*
*
..
Scalar
Arguments
..
*
CHARACTER
DIAG
,
UPLO
*
INTEGER
INFO
,
LDA
,
N
*
..
*
..
Array
Arguments
..
*
DOUBLE PRECISION
A
(
LDA
,
*
)
*
..
*
*
*>
\
par
Purpose
:
*
=============
*>
*>
\
verbatim
*>
*>
DTRTRI
computes
the
inverse
of
a
real
upper
or
lower
triangular
*>
matrix
A
.
*>
*>
This
is
the
Level
3
BLAS
version
of
the
algorithm
.
*>
\
endverbatim
*
*
Arguments
:
*
==========
*
*>
\
param
[
in
]
UPLO
*>
\
verbatim
*>
UPLO
is
CHARACTER
*
1
*>
=
'U'
:
A
is
upper
triangular
;
*>
=
'L'
:
A
is
lower
triangular
.
*>
\
endverbatim
*>
*>
\
param
[
in
]
DIAG
*>
\
verbatim
*>
DIAG
is
CHARACTER
*
1
*>
=
'N'
:
A
is
non
-
unit
triangular
;
*>
=
'U'
:
A
is
unit
triangular
.
*>
\
endverbatim
*>
*>
\
param
[
in
]
N
*>
\
verbatim
*>
N
is
INTEGER
*>
The
order
of
the
matrix
A
.
N
>=
0.
*>
\
endverbatim
*>
*>
\
param
[
in
,
out
]
A
*>
\
verbatim
*>
A
is
DOUBLE PRECISION
array
,
dimension
(
LDA
,
N
)
*>
On
entry
,
the
triangular
matrix
A
.
If
UPLO
=
'U'
,
the
*>
leading
N
-
by
-
N
upper
triangular
part
of
the
array
A
contains
*>
the
upper
triangular
matrix
,
and
the
strictly
lower
*>
triangular
part
of
A
is
not
referenced
.
If
UPLO
=
'L'
,
the
*>
leading
N
-
by
-
N
lower
triangular
part
of
the
array
A
contains
*>
the
lower
triangular
matrix
,
and
the
strictly
upper
*>
triangular
part
of
A
is
not
referenced
.
If
DIAG
=
'U'
,
the
*>
diagonal
elements
of
A
are
also
not
referenced
and
are
*>
assumed
to
be
1.
*>
On
exit
,
the
(
triangular
)
inverse
of
the
original
matrix
,
in
*>
the
same
storage
format
.
*>
\
endverbatim
*>
*>
\
param
[
in
]
LDA
*>
\
verbatim
*>
LDA
is
INTEGER
*>
The
leading
dimension
of
the
array
A
.
LDA
>=
max
(
1
,
N
)
.
*>
\
endverbatim
*>
*>
\
param
[
out
]
INFO
*>
\
verbatim
*>
INFO
is
INTEGER
*>
=
0
:
successful
exit
*>
<
0
:
if
INFO
=
-
i
,
the
i
-
th
argument
had
an
illegal
value
*>
>
0
:
if
INFO
=
i
,
A
(
i
,
i
)
is
exactly
zero
.
The
triangular
*>
matrix
is
singular
and
its
inverse
can
not
be
computed
.
*>
\
endverbatim
*
*
Authors
:
*
========
*
*>
\
author
Univ
.
of
Tennessee
*>
\
author
Univ
.
of
California
Berkeley
*>
\
author
Univ
.
of
Colorado
Denver
*>
\
author
NAG
Ltd
.
*
*>
\
date
November
2011
*
*>
\
ingroup
doubleOTHERcomputational
*
*
=====================================================================
SUBROUTINE
DTRTRI
(
UPLO
,
DIAG
,
N
,
A
,
LDA
,
INFO
)
*
*
--
LAPACK
computational
routine
(
version
3.4.0
)
--
*
--
LAPACK
is
a
software
package
provided
by
Univ
.
of
Tennessee
,
--
*
--
Univ
.
of
California
Berkeley
,
Univ
.
of
Colorado
Denver
and
NAG
Ltd
..
--
*
November
2011
*
*
..
Scalar
Arguments
..
CHARACTER
DIAG
,
UPLO
INTEGER
INFO
,
LDA
,
N
*
..
*
..
Array
Arguments
..
DOUBLE PRECISION
A
(
LDA
,
*
)
*
..
*
*
=====================================================================
*
*
..
Parameters
..
DOUBLE PRECISION
ONE
,
ZERO
PARAMETER
(
ONE
=
1.0
D
+
0
,
ZERO
=
0.0
D
+
0
)
*
..
*
..
Local
Scalars
..
LOGICAL
NOUNIT
,
UPPER
INTEGER
J
,
JB
,
NB
,
NN
*
..
*
..
External
Functions
..
LOGICAL
LSAME
INTEGER
ILAENV
EXTERNAL
LSAME
,
ILAENV
*
..
*
..
External
Subroutines
..
EXTERNAL
DTRMM
,
DTRSM
,
DTRTI2
,
XERBLA
*
..
*
..
Intrinsic
Functions
..
INTRINSIC
MAX
,
MIN
*
..
*
..
Executable
Statements
..
*
*
Test
the
input
parameters
.
*
INFO
=
0
UPPER
=
LSAME
(
UPLO
,
'U'
)
NOUNIT
=
LSAME
(
DIAG
,
'N'
)
IF
(
.NOT.
UPPER
.AND.
.NOT.
LSAME
(
UPLO
,
'L'
)
)
THEN
INFO
=
-
1
ELSE IF
(
.NOT.
NOUNIT
.AND.
.NOT.
LSAME
(
DIAG
,
'U'
)
)
THEN
INFO
=
-
2
ELSE IF
(
N
.LT.
0
)
THEN
INFO
=
-
3
ELSE IF
(
LDA
.LT.
MAX
(
1
,
N
)
)
THEN
INFO
=
-
5
END IF
IF
(
INFO
.NE.
0
)
THEN
CALL
XERBLA
(
'DTRTRI'
,
-
INFO
)
RETURN
END IF
*
*
Quick
return if
possible
*
IF
(
N
.EQ.
0
)
$
RETURN
*
*
Check
for
singularity
if
non
-
unit
.
*
IF
(
NOUNIT
)
THEN
DO
10
INFO
=
1
,
N
IF
(
A
(
INFO
,
INFO
)
.EQ.
ZERO
)
$
RETURN
10
CONTINUE
INFO
=
0
END IF
*
*
Determine
the
block
size
for
this
environment
.
*
NB
=
ILAENV
(
1
,
'DTRTRI'
,
UPLO
//
DIAG
,
N
,
-
1
,
-
1
,
-
1
)
IF
(
NB
.LE.
1
.OR.
NB
.GE.
N
)
THEN
*
*
Use
unblocked
code
*
CALL
DTRTI2
(
UPLO
,
DIAG
,
N
,
A
,
LDA
,
INFO
)
ELSE
*
*
Use
blocked
code
*
IF
(
UPPER
)
THEN
*
*
Compute
inverse
of
upper
triangular
matrix
*
DO
20
J
=
1
,
N
,
NB
JB
=
MIN
(
NB
,
N
-
J
+
1
)
*
*
Compute
rows
1
:
j
-
1
of
current
block
column
*
CALL
DTRMM
(
'Left'
,
'Upper'
,
'No transpose'
,
DIAG
,
J
-
1
,
$
JB
,
ONE
,
A
,
LDA
,
A
(
1
,
J
),
LDA
)
CALL
DTRSM
(
'Right'
,
'Upper'
,
'No transpose'
,
DIAG
,
J
-
1
,
$
JB
,
-
ONE
,
A
(
J
,
J
),
LDA
,
A
(
1
,
J
),
LDA
)
*
*
Compute
inverse
of
current
diagonal
block
*
CALL
DTRTI2
(
'Upper'
,
DIAG
,
JB
,
A
(
J
,
J
),
LDA
,
INFO
)
20
CONTINUE
ELSE
*
*
Compute
inverse
of
lower
triangular
matrix
*
NN
=
(
(
N
-
1
)
/
NB
)
*
NB
+
1
DO
30
J
=
NN
,
1
,
-
NB
JB
=
MIN
(
NB
,
N
-
J
+
1
)
IF
(
J
+
JB
.LE.
N
)
THEN
*
*
Compute
rows
j
+
jb
:
n
of
current
block
column
*
CALL
DTRMM
(
'Left'
,
'Lower'
,
'No transpose'
,
DIAG
,
$
N
-
J
-
JB
+
1
,
JB
,
ONE
,
A
(
J
+
JB
,
J
+
JB
),
LDA
,
$
A
(
J
+
JB
,
J
),
LDA
)
CALL
DTRSM
(
'Right'
,
'Lower'
,
'No transpose'
,
DIAG
,
$
N
-
J
-
JB
+
1
,
JB
,
-
ONE
,
A
(
J
,
J
),
LDA
,
$
A
(
J
+
JB
,
J
),
LDA
)
END IF
*
*
Compute
inverse
of
current
diagonal
block
*
CALL
DTRTI2
(
'Lower'
,
DIAG
,
JB
,
A
(
J
,
J
),
LDA
,
INFO
)
30
CONTINUE
END IF
END IF
*
RETURN
*
*
End
of
DTRTRI
*
END
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