spotf2(3S)

NAME
     SPOTF2 - compute the Cholesky factorization of a real symmetric positive
     definite matrix A

SYNOPSIS
     SUBROUTINE SPOTF2( UPLO, N, A, LDA, INFO )

         CHARACTER      UPLO

         INTEGER        INFO, LDA, N

         REAL           A( LDA, * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     SPOTF2 computes the Cholesky factorization of a real symmetric positive
     definite matrix A. The factorization has the form
        A = U' * U ,  if UPLO = 'U', or
        A = L  * L',  if UPLO = 'L',
     where U is an upper triangular matrix and L is lower triangular.

     This is the unblocked version of the algorithm, calling Level 2 BLAS.


ARGUMENTS
     UPLO    (input) CHARACTER*1
             Specifies whether the upper or lower triangular part of the
             symmetric matrix A is stored.  = 'U':  Upper triangular
             = 'L':  Lower triangular

     N       (input) INTEGER
             The order of the matrix A.  N >= 0.

     A       (input/output) REAL array, dimension (LDA,N)
             On entry, the symmetric matrix A.  If UPLO = 'U', the leading 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 = 'L', the leading 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.

             On exit, if INFO = 0, the factor U or L from the Cholesky
             factorization A = U'*U  or A = L*L'.

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

     INFO    (output) INTEGER
             = 0: successful exit
             < 0: if INFO = -k, the k-th argument had an illegal value
             > 0: if INFO = k, the leading minor of order k is not positive
             definite, and the factorization could not be completed.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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