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PROGRAM TEST
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IMPLICIT NONE
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C
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INTEGER LDA, N
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PARAMETER (N = 4)
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PARAMETER (LDA = N)
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C
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DOUBLE PRECISION A(LDA,N)
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INTEGER ICOL, INFO, IROW
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C
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EXTERNAL DPOTRF, DPOTRI
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INTRINSIC ABS
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C
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C Initialize the array A to store in symmetric form the
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C 4x4 symmetric positive definite coefficient matrix A
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C shown below.
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C
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C 2 1 0 0
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C A = 1 2 1 0
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C 0 1 2 1
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C 0 0 1 1
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C
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DATA A / 2.0D0, 3*8D8, 1.0D0, 2.0D0, 2*8D8, 0.0D0, 1.0D0,
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$ 2.0D0, 8D8, 0.0D0, 0.0D0, 1.0D0, 1.0D0 /
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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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DO 100, IROW = 1, N
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PRINT 1010, (A(ICOL,IROW), ICOL = 1, IROW - 1),
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$ (A(IROW,ICOL), ICOL = IROW, N)
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100 CONTINUE
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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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C
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C Cholesky factor A.
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C
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CALL DPOTRF ('UPPER TRIANGLE OF A STORED', N, A, LDA, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1030, 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 compute the inverse of A and
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C print the inverse thus computed.
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C
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CALL DPOTRI ('UPPER TRIANGLE OF A STORED', N, A, LDA, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1040, ABS(INFO)
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STOP 2
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END IF
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PRINT 1050
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DO 200, IROW = 1, N
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PRINT 1010, (A(ICOL,IROW), ICOL = 1, IROW - 1),
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$ (A(IROW,ICOL), ICOL = IROW, N)
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200 CONTINUE
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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 symmetric form: (* in unused elements)')
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1030 FORMAT (1X, 'Error factoring A, INFO = ', I5)
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1040 FORMAT (1X, 'Error computing inverse of A, INFO = ', I5)
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1050 FORMAT (/1X, 'A**(-1):')
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C
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END
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