DPBFA(3F)							     DPBFA(3F)

NAME    [Toc]    [Back]

     DPBFA   - 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    [Toc]    [Back]

      SUBROUTINE DPBFA(ABD,LDA,N,M,INFO)

DESCRIPTION    [Toc]    [Back]

     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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