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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, LDQ, LDWORK, N, NDIAG
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PARAMETER (N = 4)
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PARAMETER (NDIAG = 1)
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PARAMETER (LDA = NDIAG + 1)
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PARAMETER (LDEVEC = N)
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PARAMETER (LDIWRK = 5 * N)
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PARAMETER (LDWORK = 7 * N)
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PARAMETER (LDQ = N)
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C
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DOUBLE PRECISION A(LDA,N), EVALS(N), EVECS(LDEVEC,N), TEMP
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DOUBLE PRECISION Q(LDQ,N), 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 DSBEVX
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INTRINSIC ABS
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C
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C Initialize the array A to store the symmetric tridiagonal
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C matrix A shown below.
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C
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C 1 0 0 0
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C A = 0 2 1 0
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C 0 1 2 0
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C 0 0 0 1
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C
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DATA A / 8D8, 1.0D0, 0.0D0, 2.0D0, 1.0D0, 2.0D0, 0.0D0,
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$ 1.0D0 /
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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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DO 100, IROW = 1, LDA
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PRINT 1010, (A(IROW,ICOL), ICOL = 1, N)
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100 CONTINUE
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C
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C Compute the eigenvalues and right eigenvectors of A.
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C
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CALL DSBEVX ('VECTORS AND EIGENVALUES', 'ALL EIGENVALUES',
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$ 'UPPER TRIANGLE A STORED', N, NDIAG, A, LDA,
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$ Q, LDQ, TEMP, TEMP, ITEMP, ITEMP, 0.0D0,
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$ NFOUND, EVALS, EVECS, LDEVEC, WORK, IWORK,
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$ 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, ABS(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 (4(3X, F9.6))
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1020 FORMAT (/1X,
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$ 'A in symmetric banded form: '
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$ ' (* in unused elements)')
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1030 FORMAT (/1X, 'Illegal argument to DSBEVX, argument #', I2)
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1040 FORMAT (/1X, 'Convergence failure, INFO = ', I2)
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1050 FORMAT (/1X, 'Eigenvalue', 10X, 'Eigenvector**T')
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1060 FORMAT (1X, F7.2, 6X, '[', 3(F5.3, ', '), F5.3, ']')
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C
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END
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