DPBFA(3F)DPBFA(3F)NAMEDPBFA - DPBFA factors a double precision symmetric positive definite
matrix stored in band form.
DPBFA is usually called by DPBCO, but it can be called directly with a
saving in time if RCOND is not needed.
SYNOPSYS
SUBROUTINE DPBFA(ABD,LDA,N,M,INFO)
DESCRIPTION
On Entry
ABD DOUBLE PRECISION(LDA, N)
the matrix to be factored. The columns of the upper
triangle are stored in the columns of ABD and the
diagonals of the upper triangle are stored in the
rows of ABD . See the comments below for details.
LDA INTEGER
the leading dimension of the array ABD .
LDA must be .GE. M + 1 .
N INTEGER
the order of the matrix A .
M INTEGER
the number of diagonals above the main diagonal.
0 .LE. M .LT. N . On Return
ABD an upper triangular matrix R , stored in band
form, so that A = TRANS(R)*R .
INFO INTEGER
= 0 for normal return.
= K if the leading minor of order K is not
positive definite. Band Storage
If A is a symmetric positive definite band matrix,
the following program segment will set up the input.
M = (band width above diagonal)
DO 20 J = 1, N
I1 = MAX0(1, J-M)
DO 10 I = I1, J
K = I-J+M+1
ABD(K,J) = A(I,J)
10 CONTINUE
20 CONTINUE LINPACK. This version dated 08/14/78 . Cleve Moler,
University of New Mexico, Argonne National Lab. Subroutines and
Functions BLAS DDOT Fortran MAX0,DSQRT
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