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PROGRAM TEST
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IMPLICIT NONE
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C
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INTEGER LDEVEC, LDIWRK, LDWORK, LENGTA, N
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PARAMETER (N = 3)
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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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PARAMETER (LENGTA = (N * N + N) / 2)
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C
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DOUBLE PRECISION A(LENGTA), 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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INTRINSIC ABS
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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, 1.0D0, 9.0D0, 1.0D0, 1.0D0, 9.0D0 /
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C
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PRINT 1000
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PRINT 1010, A(1), A(2), A(4)
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PRINT 1010, A(2), A(3), A(5)
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PRINT 1010, A(4), A(5), A(6)
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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 6 - 9 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 DSPEVX for
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C arguments 6 - 9 are of the correct type. Arguments 6 and 7
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C take the place of double precision values, so TEMP is
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C declared double precision. Arguments 8 and 9 take the place
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C of integer arguments, so ITEMP is declared integer. Even
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C though these arguments are not referenced, passing arguments
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C of the wrong type may cause run time errors due to the
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C alignment of the arguments in memory.
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C
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CALL DSPEVX ('VALUES AND VECTORS', 'ALL EIGENVALUES',
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$ 'UPPER TRIANGULAR A', N, A, TEMP, TEMP, ITEMP,
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$ ITEMP, 0.0D0, NFOUND, EVALS, EVECS, LDEVEC,
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$ WORK, 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 1020, ABS(INFO)
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STOP 1
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ELSE
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PRINT 1030, 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 1040
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DO 120, ICOL = 1, N
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PRINT 1050, 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:')
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1010 FORMAT (3(3X, F4.1))
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1020 FORMAT (/1X, 'Illegal argument to DSPEVX, argument #', I2)
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1030 FORMAT (/1X, 'Convergence failure, INFO = ', I2)
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1040 FORMAT (/1X, 'Eigenvalue', 4X, 'Eigenvector**T')
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1050 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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