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PROGRAM TEST
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IMPLICIT NONE
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C
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INTEGER LDA, LDEVEC, LDIWRK, LDWORK, N
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PARAMETER (N = 3)
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PARAMETER (LDA = N)
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PARAMETER (LDEVEC = N)
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PARAMETER (LDIWRK = 5 * N)
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PARAMETER (LDWORK = 8 * N)
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C
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DOUBLE PRECISION A(LDA,N), TEMP, EVALS(N), EVECS(LDEVEC,N)
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DOUBLE PRECISION WORK(LDWORK)
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INTEGER ICOL, IFAIL(N), INFO, IROW, ITEMP
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INTEGER IWORK(LDIWRK), NFOUND
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C
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EXTERNAL DSYEVX
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C
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C Initialize the array A to store the matrix A shown below.
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C
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C 9 1 1
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C A = 1 9 1
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C 1 1 9
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C
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DATA A / 9.0D0, 8D8, 8D8, 1.0D0, 9.0D0, 8D8, 1.0D0, 1.0D0,
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$ 9.0D0 /
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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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DO 110, IROW = 1, N
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PRINT 1010, (A(IROW,ICOL), ICOL = 1, N)
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110 CONTINUE
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C
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C Compute the eigenvalues and eigenvectors of A.
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C
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C Arguments 7 - 10 are not used because RANGE (argument 2)
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C indicates that all eigenvalues should be found. Note
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C however that the scratch values passed into DSYEVX for
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C arguments 7 - 10 are of the correct type. Arguments 7
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C and 8 take the place of double precision values, so TEMP
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C is declared double precision. Arguments 9 and 10 take the
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C place of integer arguments, so ITEMP is declared integer.
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C Even though these arguments are not referenced, passing
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C arguments of the wrong type may cause run time errors due
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C to the alignment of the arguments in memory.
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C
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CALL DSYEVX ('VALUES AND VECTORS', 'ALL EIGENVALUES',
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$ 'UPPER TRIANGULAR A', N, A, LDA, TEMP, TEMP,
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$ ITEMP, ITEMP, 0.0D0, NFOUND, EVALS, EVECS,
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$ LDEVEC, WORK, LDWORK, IWORK, IFAIL, INFO)
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IF (INFO .NE. 0) THEN
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IF (INFO .LT. 0) THEN
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PRINT 1030, -INFO
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STOP 1
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ELSE
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PRINT 1040, INFO
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STOP 2
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END IF
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END IF
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C
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C Print the eigenvalues and eigenvectors.
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C
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PRINT 1050
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DO 120, ICOL = 1, N
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PRINT 1060, EVALS(ICOL), (EVECS(IROW,ICOL), IROW = 1, N)
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120 CONTINUE
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C
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1000 FORMAT (1X, 'A in full form:')
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1010 FORMAT (3(3X, F4.1))
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1020 FORMAT (/1X, 'A in symmetric form: (* in unused elements)')
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1030 FORMAT (/1X, 'Illegal argument to DSYEVX, argument #', I2)
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1040 FORMAT (/1X, 'Convergence failure, INFO = ', I2)
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1050 FORMAT (/1X, 'Eigenvalue', 4X, 'Eigenvector**T')
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1060 FORMAT (1X, F7.2, 5X, '[', F4.2, ', ', F4.2, ', ',
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$ F4.2, ']')
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C
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END
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