Contents

# ?sytrs_rook

Solves a system of linear equations with a UDU- or LDL-factored symmetric coefficient matrix.

## Syntax

Include Files
• mkl.h
Description
The routine solves a system of linear equations
A*X
=
B
with a symmetric matrix
A
, using the factorization
A
=
U*D*U
T
or
A
=
L*D*L
T
computed by
?sytrf_rook
.
Input Parameters
matrix_layout
Specifies whether matrix storage layout for array
b
is row major (
LAPACK_ROW_MAJOR
) or column major (
LAPACK_COL_MAJOR
).
uplo
Must be
'U'
or
'L'
.
Indicates how the input matrix
A
has been factored:
If
uplo
=
'U'
, the factorization is of the form
A
=
U*D*U
T
.
If
uplo
=
'L'
, the factorization is of the form
A
=
L*D*L
T
.
n
The order of matrix
A
;
n
0.
nrhs
The number of right-hand sides;
nrhs
0.
ipiv
Array, size at least
max(1,
n
)
. The
ipiv
array, as returned by
?sytrf_rook
.
a
,
b
Arrays:
a
, size (
lda
*
n
)
,
b
size (
ldb
*
nrhs
)
.
The array
a
contains the block diagonal matrix
D
and the multipliers used to obtain
U
or
L
as computed by
?sytrf_rook
(see
uplo
).
The array
b
contains the matrix
B
whose columns are the right-hand sides for the system of equations.
lda
a
;
lda
max(1,
n
)
.
ldb
b
;
ldb
max(1,
n
) for column major layout and
ldb
nrhs
) for row major layout
.
Output Parameters
b
Overwritten by the solution matrix
X
.
Return Values
This function returns a value
info
.
If
info
=0
, the execution is successful.
If
info
=
-i
, the
i
-th parameter had an illegal value.
Application Notes
The total number of floating-point operations for one right-hand side vector is approximately
2
n
2
for real flavors or
8
n
2
for complex flavors.

#### Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.