 LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ slauu2()

 subroutine slauu2 ( character UPLO, integer N, real, dimension( lda, * ) A, integer LDA, integer INFO )

SLAUU2 computes the product UUH or LHL, where U and L are upper or lower triangular matrices (unblocked algorithm).

Purpose:
``` SLAUU2 computes the product U * U**T or L**T * L, where the triangular
factor U or L is stored in the upper or lower triangular part of
the array A.

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

This is the unblocked form of the algorithm, calling Level 2 BLAS.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 Specifies whether the triangular factor stored in the array A is upper or lower triangular: = 'U': Upper triangular = 'L': Lower triangular``` [in] N ``` N is INTEGER The order of the triangular factor U or L. N >= 0.``` [in,out] A ``` A is REAL array, dimension (LDA,N) On entry, the triangular factor U or L. On exit, if UPLO = 'U', the upper triangle of A is overwritten with the upper triangle of the product U * U**T; if UPLO = 'L', the lower triangle of A is overwritten with the lower triangle of the product L**T * L.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [out] INFO ``` INFO is INTEGER = 0: successful exit < 0: if INFO = -k, the k-th argument had an illegal value```

Definition at line 101 of file slauu2.f.

102 *
103 * -- LAPACK auxiliary routine --
104 * -- LAPACK is a software package provided by Univ. of Tennessee, --
105 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
106 *
107 * .. Scalar Arguments ..
108  CHARACTER UPLO
109  INTEGER INFO, LDA, N
110 * ..
111 * .. Array Arguments ..
112  REAL A( LDA, * )
113 * ..
114 *
115 * =====================================================================
116 *
117 * .. Parameters ..
118  REAL ONE
119  parameter( one = 1.0e+0 )
120 * ..
121 * .. Local Scalars ..
122  LOGICAL UPPER
123  INTEGER I
124  REAL AII
125 * ..
126 * .. External Functions ..
127  LOGICAL LSAME
128  REAL SDOT
129  EXTERNAL lsame, sdot
130 * ..
131 * .. External Subroutines ..
132  EXTERNAL sgemv, sscal, xerbla
133 * ..
134 * .. Intrinsic Functions ..
135  INTRINSIC max
136 * ..
137 * .. Executable Statements ..
138 *
139 * Test the input parameters.
140 *
141  info = 0
142  upper = lsame( uplo, 'U' )
143  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
144  info = -1
145  ELSE IF( n.LT.0 ) THEN
146  info = -2
147  ELSE IF( lda.LT.max( 1, n ) ) THEN
148  info = -4
149  END IF
150  IF( info.NE.0 ) THEN
151  CALL xerbla( 'SLAUU2', -info )
152  RETURN
153  END IF
154 *
155 * Quick return if possible
156 *
157  IF( n.EQ.0 )
158  \$ RETURN
159 *
160  IF( upper ) THEN
161 *
162 * Compute the product U * U**T.
163 *
164  DO 10 i = 1, n
165  aii = a( i, i )
166  IF( i.LT.n ) THEN
167  a( i, i ) = sdot( n-i+1, a( i, i ), lda, a( i, i ), lda )
168  CALL sgemv( 'No transpose', i-1, n-i, one, a( 1, i+1 ),
169  \$ lda, a( i, i+1 ), lda, aii, a( 1, i ), 1 )
170  ELSE
171  CALL sscal( i, aii, a( 1, i ), 1 )
172  END IF
173  10 CONTINUE
174 *
175  ELSE
176 *
177 * Compute the product L**T * L.
178 *
179  DO 20 i = 1, n
180  aii = a( i, i )
181  IF( i.LT.n ) THEN
182  a( i, i ) = sdot( n-i+1, a( i, i ), 1, a( i, i ), 1 )
183  CALL sgemv( 'Transpose', n-i, i-1, one, a( i+1, 1 ), lda,
184  \$ a( i+1, i ), 1, aii, a( i, 1 ), lda )
185  ELSE
186  CALL sscal( i, aii, a( i, 1 ), lda )
187  END IF
188  20 CONTINUE
189  END IF
190 *
191  RETURN
192 *
193 * End of SLAUU2
194 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:79
real function sdot(N, SX, INCX, SY, INCY)
SDOT
Definition: sdot.f:82
subroutine sgemv(TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
SGEMV
Definition: sgemv.f:156
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