Program f07hafe
! F07HAF Example Program Text
! Mark 29.2 Release. NAG Copyright 2023.
! .. Use Statements ..
Use nag_library, Only: dpbsv, nag_wp, x04cef
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
Character (1), Parameter :: uplo = 'U'
! .. Local Scalars ..
Integer :: i, ifail, info, j, kd, ldab, n
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: ab(:,:), b(:)
! .. Intrinsic Procedures ..
Intrinsic :: max, min
! .. Executable Statements ..
Write (nout,*) 'F07HAF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n, kd
ldab = kd + 1
Allocate (ab(ldab,n),b(n))
! Read the upper or lower triangular part of the band matrix A
! from data file
If (uplo=='U') Then
Read (nin,*)((ab(kd+1+i-j,j),j=i,min(n,i+kd)),i=1,n)
Else If (uplo=='L') Then
Read (nin,*)((ab(1+i-j,j),j=max(1,i-kd),i),i=1,n)
End If
! Read b from data file
Read (nin,*) b(1:n)
! Solve the equations Ax = b for x
! The NAG name equivalent of dpbsv is f07haf
Call dpbsv(uplo,n,kd,1,ab,ldab,b,n,info)
If (info==0) Then
! Print solution
Write (nout,*) 'Solution'
Write (nout,99999) b(1:n)
! Print details of factorization
Write (nout,*)
Flush (nout)
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
If (uplo=='U') Then
Call x04cef(n,n,0,kd,ab,ldab,'Cholesky factor U',ifail)
Else If (uplo=='L') Then
Call x04cef(n,n,kd,0,ab,ldab,'Cholesky factor L',ifail)
End If
Else
Write (nout,99998) 'The leading minor of order ', info, &
' is not positive definite'
End If
99999 Format ((3X,7F11.4))
99998 Format (1X,A,I3,A)
End Program f07hafe