NAME

       ssygs2.f -

SYNOPSIS

   Functions/Subroutines
       subroutine ssygs2 (ITYPE, UPLO, N, A, LDA, B, LDB, INFO)
           SSYGS2 reduces a symmetric definite generalized eigenproblem to standard form, using
           the factorization results obtained from spotrf (unblocked algorithm).

Function/Subroutine Documentation

   subroutine ssygs2 (integerITYPE, characterUPLO, integerN, real, dimension( lda, * )A,
       integerLDA, real, dimension( ldb, * )B, integerLDB, integerINFO)
       SSYGS2 reduces a symmetric definite generalized eigenproblem to standard form, using the
       factorization results obtained from spotrf (unblocked algorithm).

       Purpose:

            SSYGS2 reduces a real symmetric-definite generalized eigenproblem
            to standard form.

            If ITYPE = 1, the problem is A*x = lambda*B*x,
            and A is overwritten by inv(U**T)*A*inv(U) or inv(L)*A*inv(L**T)

            If ITYPE = 2 or 3, the problem is A*B*x = lambda*x or
            B*A*x = lambda*x, and A is overwritten by U*A*U**T or L**T *A*L.

            B must have been previously factorized as U**T *U or L*L**T by SPOTRF.

       Parameters:
           ITYPE

                     ITYPE is INTEGER
                     = 1: compute inv(U**T)*A*inv(U) or inv(L)*A*inv(L**T);
                     = 2 or 3: compute U*A*U**T or L**T *A*L.

           UPLO

                     UPLO is CHARACTER*1
                     Specifies whether the upper or lower triangular part of the
                     symmetric matrix A is stored, and how B has been factorized.
                     = 'U':  Upper triangular
                     = 'L':  Lower triangular

           N

                     N is INTEGER
                     The order of the matrices A and B.  N >= 0.

           A

                     A is 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 transformed matrix, stored in the
                     same format as A.

           LDA

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

           B

                     B is REAL array, dimension (LDB,N)
                     The triangular factor from the Cholesky factorization of B,
                     as returned by SPOTRF.

           LDB

                     LDB is INTEGER
                     The leading dimension of the array B.  LDB >= max(1,N).

           INFO

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

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       Definition at line 128 of file ssygs2.f.

Author

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