## Developer Reference

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

# ?potrf2

Computes Cholesky factorization using a recursive algorithm.

## Syntax

Include Files
• mkl.fi
Description
?potrf2
computes the Cholesky factorization of a real or complex symmetric positive definite matrix
A
using the recursive algorithm.
The factorization has the form
for real flavors:
A
=
U
T
*
U
, if
uplo
= 'U', or
A
=
L
*
L
T
, if
uplo
= 'L',
for complex flavors:
A
=
U
H
*
U
, if
uplo
= 'U',
or
A
=
L
*
L
H
, if
uplo
= 'L',
where
U
is an upper triangular matrix and
L
is lower triangular.
This is the recursive version of the algorithm. It divides the matrix into four submatrices: where
A11
is
n1
by
n1
and
A22
is
n2
by
n2
, with
n1
=
n
/2 and
n2
=
n
-
n1
.
The subroutine calls itself to factor
A11
. Update and scale
A21
or
A12
, update
A22
then call itself to factor
A22
.
Input Parameters
uplo
CHARACTER*1.
= 'U': Upper triangle of
A
is stored;
= 'L': Lower triangle of
A
is stored.
n
INTEGER.
The order of the matrix
A
.
n
0.
a
REAL
for
spotrf2
DOUBLE PRECISION
for
dpotrf2
COMPLEX
for
cpotrf2
DOUBLE COMPLEX
for
zpotrf2
Array, size
(
lda
,
n
)
.
On entry, the symmetric matrix
A
.
If
uplo
n
-by-
n
upper triangular part of
a
contains the upper triangular part of the matrix
A
, and the strictly lower triangular part of
a
is not referenced.
If
uplo
n
-by-
n
lower triangular part of
a
contains the lower triangular part of the matrix
A
, and the strictly upper triangular part of
a
is not referenced.
lda
INTEGER.
The leading dimension of the array
a
.