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PROGRAM TEST
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IMPLICIT NONE
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C
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INTEGER LDA, LDB, N, NDIAG, NRHS
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PARAMETER (N = 4)
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PARAMETER (NDIAG = 1)
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PARAMETER (NRHS = 1)
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PARAMETER (LDA = NDIAG + 1)
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PARAMETER (LDB = N)
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C
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DOUBLE PRECISION A(LDA,N), B(LDB,NRHS)
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INTEGER ICOL, INFO, IROW
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C
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EXTERNAL DPBTRF, DPBTRS
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INTRINSIC ABS
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C
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C Initialize the array A to store in symmetric banded form
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C the 4x4 symmetric positive definite coefficient matrix A
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C with one subdiagonal and one superdiagonal shown below.
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C Initialize the array B to store the right hand side
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C vector b shown below.
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C
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C 2 -1 0 0 6
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C A = -1 2 -1 0 b = 12
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C 0 -1 2 -1 12
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C 0 0 -1 2 6
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C
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DATA A / 8D8, 2.0D0, -1.0D0, 2.0D0,
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$ -1.0D0, 2.0D0, -1.0D0, 2.0D0 /
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DATA B / 6.0D0, 1.2D1, 1.2D1, 6.0D0 /
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C
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C Print the initial values of the arrays.
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C
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PRINT 1000
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PRINT 1010, A(2,1), A(1,2), 0.0D0, 0.0D0
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PRINT 1010, A(1,2), A(2,2), A(1,3), 0.0D0
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PRINT 1010, 0.0D0, A(1,3), A(2,3), A(1,4)
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PRINT 1010, 0.0D0, 0.0D0, A(1,4), A(2,4)
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PRINT 1020
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PRINT 1010, ((A(IROW,ICOL), ICOL = 1, N), IROW = 1, LDA)
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PRINT 1030
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PRINT 1040, B
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C
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C Cholesky factor A.
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C
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CALL DPBTRF ('UPPER TRIANGLE OF A STORED', N, NDIAG, A, LDA,
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$ INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1050, INFO
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STOP 1
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END IF
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C
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C Use the factored form of A to solve Ax=b then print
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C the result.
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C
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CALL DPBTRS ('UPPER TRIANGLE OF A STORED', N, NDIAG, NRHS,
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$ A, LDA, B, LDB, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1060, ABS(INFO)
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STOP 1
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END IF
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PRINT 1070
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PRINT 1040, B
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C
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1000 FORMAT (1X, 'A in full form:')
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1010 FORMAT (4(3X, F6.3))
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1020 FORMAT (/1X, 'A in banded form: (* in unused elements)')
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1030 FORMAT (/1X, 'b:')
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1040 FORMAT (1X, F6.2)
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1050 FORMAT (1X, 'Error factoring A, INFO = ', I5)
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1060 FORMAT (1X, 'Illegal argument to DPBTRS, argument #', I1)
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1070 FORMAT (/1X, 'x:')
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C
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END
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