sppfa.f
SUBROUTINE SPPFA (AP, N, INFO)
C***BEGIN PROLOGUE SPPFA
C***PURPOSE Factor a real symmetric positive definite matrix stored in
C packed form.
C***LIBRARY SLATEC (LINPACK)
C***CATEGORY D2B1B
C***TYPE SINGLE PRECISION (SPPFA-S, DPPFA-D, CPPFA-C)
C***KEYWORDS LINEAR ALGEBRA, LINPACK, MATRIX FACTORIZATION, PACKED,
C POSITIVE DEFINITE
C***AUTHOR Moler, C. B., (U. of New Mexico)
C***DESCRIPTION
C
C SPPFA factors a real symmetric positive definite matrix
C stored in packed form.
C
C SPPFA is usually called by SPPCO, but it can be called
C directly with a saving in time if RCOND is not needed.
C (Time for SPPCO) = (1 + 18/N)*(Time for SPPFA) .
C
C On Entry
C
C AP REAL (N*(N+1)/2)
C the packed form of a symmetric matrix A . The
C columns of the upper triangle are stored sequentially
C in a one-dimensional array of length N*(N+1)/2 .
C See comments below for details.
C
C N INTEGER
C the order of the matrix A .
C
C On Return
C
C AP an upper triangular matrix R , stored in packed
C form, so that A = TRANS(R)*R .
C
C INFO INTEGER
C = 0 for normal return.
C = K if the leading minor of order K is not
C positive definite.
C
C
C Packed Storage
C
C The following program segment will pack the upper
C triangle of a symmetric matrix.
C
C K = 0
C DO 20 J = 1, N
C DO 10 I = 1, J
C K = K + 1
C AP(K) = A(I,J)
C 10 CONTINUE
C 20 CONTINUE
C
C***REFERENCES J. J. Dongarra, J. R. Bunch, C. B. Moler, and G. W.
C Stewart, LINPACK Users' Guide, SIAM, 1979.
C***ROUTINES CALLED SDOT
C***REVISION HISTORY (YYMMDD)
C 780814 DATE WRITTEN
C 890831 Modified array declarations. (WRB)
C 890831 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 900326 Removed duplicate information from DESCRIPTION section.
C (WRB)
C 920501 Reformatted the REFERENCES section. (WRB)
C***END PROLOGUE SPPFA