LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine spotri ( character  UPLO,
integer  N,
real, dimension( lda, * )  A,
integer  LDA,
integer  INFO 
)

SPOTRI

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Purpose: 
 SPOTRI computes the inverse of a real symmetric positive definite
 matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
 computed by SPOTRF.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  Upper triangle of A is stored;
          = 'L':  Lower triangle of A is stored.
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in,out]A
          A is REAL array, dimension (LDA,N)
          On entry, the triangular factor U or L from the Cholesky
          factorization A = U**T*U or A = L*L**T, as computed by
          SPOTRF.
          On exit, the upper or lower triangle of the (symmetric)
          inverse of A, overwriting the input factor U or 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 = -i, the i-th argument had an illegal value
          > 0:  if INFO = i, the (i,i) element of the factor U or L is
                zero, and the inverse could not be computed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 97 of file spotri.f.

97 *
98 * -- LAPACK computational routine (version 3.4.0) --
99 * -- LAPACK is a software package provided by Univ. of Tennessee, --
100 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
101 * November 2011
102 *
103 * .. Scalar Arguments ..
104  CHARACTER uplo
105  INTEGER info, lda, n
106 * ..
107 * .. Array Arguments ..
108  REAL a( lda, * )
109 * ..
110 *
111 * =====================================================================
112 *
113 * .. External Functions ..
114  LOGICAL lsame
115  EXTERNAL lsame
116 * ..
117 * .. External Subroutines ..
118  EXTERNAL slauum, strtri, xerbla
119 * ..
120 * .. Intrinsic Functions ..
121  INTRINSIC max
122 * ..
123 * .. Executable Statements ..
124 *
125 * Test the input parameters.
126 *
127  info = 0
128  IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
129  info = -1
130  ELSE IF( n.LT.0 ) THEN
131  info = -2
132  ELSE IF( lda.LT.max( 1, n ) ) THEN
133  info = -4
134  END IF
135  IF( info.NE.0 ) THEN
136  CALL xerbla( 'SPOTRI', -info )
137  RETURN
138  END IF
139 *
140 * Quick return if possible
141 *
142  IF( n.EQ.0 )
143  $ RETURN
144 *
145 * Invert the triangular Cholesky factor U or L.
146 *
147  CALL strtri( uplo, 'Non-unit', n, a, lda, info )
148  IF( info.GT.0 )
149  $ RETURN
150 *
151 * Form inv(U) * inv(U)**T or inv(L)**T * inv(L).
152 *
153  CALL slauum( uplo, n, a, lda, info )
154 *
155  RETURN
156 *
157 * End of SPOTRI
158 *
xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
strtri
subroutine strtri(UPLO, DIAG, N, A, LDA, INFO)
STRTRI
Definition: strtri.f:111
lsame
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
slauum
subroutine slauum(UPLO, N, A, LDA, INFO)
SLAUUM computes the product UUH or LHL, where U and L are upper or lower triangular matrices (blocked...
Definition: slauum.f:104

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