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SUBROUTINE SPBFA(ABD,LDA,N,M,INFO)
INTEGER LDA,N,M,INFO
REAL ABD(LDA,1)
C
C SPBFA FACTORS A REAL SYMMETRIC POSITIVE DEFINITE MATRIX
C STORED IN BAND FORM.
C
C SPBFA IS USUALLY CALLED BY SPBCO, BUT IT CAN BE CALLED
C DIRECTLY WITH A SAVING IN TIME IF RCOND IS NOT NEEDED.
C
C ON ENTRY
C
C ABD REAL(LDA, N)
C THE MATRIX TO BE FACTORED. THE COLUMNS OF THE UPPER
C TRIANGLE ARE STORED IN THE COLUMNS OF ABD AND THE
C DIAGONALS OF THE UPPER TRIANGLE ARE STORED IN THE
C ROWS OF ABD . SEE THE COMMENTS BELOW FOR DETAILS.
C
C LDA INTEGER
C THE LEADING DIMENSION OF THE ARRAY ABD .
C LDA MUST BE .GE. M + 1 .
C
C N INTEGER
C THE ORDER OF THE MATRIX A .
C
C M INTEGER
C THE NUMBER OF DIAGONALS ABOVE THE MAIN DIAGONAL.
C 0 .LE. M .LT. N .
C
C ON RETURN
C
C ABD AN UPPER TRIANGULAR MATRIX R , STORED IN BAND
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 BAND STORAGE
C
C IF A IS A SYMMETRIC POSITIVE DEFINITE BAND MATRIX,
C THE FOLLOWING PROGRAM SEGMENT WILL SET UP THE INPUT.
C
C M = (BAND WIDTH ABOVE DIAGONAL)
C DO 20 J = 1, N
C I1 = MAX0(1, J-M)
C DO 10 I = I1, J
C K = I-J+M+1
C ABD(K,J) = A(I,J)
C 10 CONTINUE
C 20 CONTINUE
C
C LINPACK. THIS VERSION DATED 08/14/78 .
C CLEVE MOLER, UNIVERSITY OF NEW MEXICO, ARGONNE NATIONAL LAB.
C
C SUBROUTINES AND FUNCTIONS
C
C BLAS SDOT
C FORTRAN MAX0,SQRT
C