## MB01XD

### Computing U' U or L L', with U and L upper and lower triangular matrices (block algorithm)

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

```  To compute the matrix product U' * U or L * L', where U and L are
upper and lower triangular matrices, respectively, stored in the
corresponding upper or lower triangular part of the array A.

If UPLO = 'U' then the upper triangle of the result is stored,
overwriting the matrix U in A.
If UPLO = 'L' then the lower triangle of the result is stored,
overwriting the matrix L in A.

```
Specification
```      SUBROUTINE MB01XD( UPLO, N, A, LDA, INFO )
C     .. Scalar Arguments ..
CHARACTER          UPLO
INTEGER            INFO, LDA, N
C     .. Array Arguments ..
DOUBLE PRECISION   A( LDA, * )

```
Arguments

Mode Parameters

```  UPLO    CHARACTER*1
Specifies which triangle (U or L) is given in the array A,
as follows:
= 'U':  the upper triangular part U is given;
= 'L':  the lower triangular part L is given.

```
Input/Output Parameters
```  N       (input) INTEGER
The order of the triangular matrices U or L.  N >= 0.

A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, if UPLO = 'U', the leading N-by-N upper
triangular part of this array must contain the upper
triangular matrix U.
On entry, if UPLO = 'L', the leading N-by-N lower
triangular part of this array must contain the lower
triangular matrix L.
On exit, if UPLO = 'U', the leading N-by-N upper
triangular part of this array contains the upper
triangular part of the product U' * U. The strictly lower
triangular part is not referenced.
On exit, if UPLO = 'L', the leading N-by-N lower
triangular part of this array contains the lower
triangular part of the product L * L'. The strictly upper
triangular part is not referenced.

LDA     INTEGER
The leading dimension of array A.  LDA >= max(1,N).

```
Error Indicator
```  INFO    INTEGER
= 0:  successful exit;
< 0:  if INFO = -i, the i-th argument had an illegal
value.

```
Method
```  The matrix product U' * U or L * L' is computed using BLAS 3
operations as much as possible (a block algorithm).

```
```  This routine is a counterpart of LAPACK Library routine DLAUUM,
which computes the matrix product U * U' or L' * L.

```
Example

Program Text

```  None
```
Program Data
```  None
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Program Results
```  None
```