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◆ _dsyev()
| void _dsyev |
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char |
jobz, |
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char |
uplo, |
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int |
n, |
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int |
lda, |
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double |
a[], |
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double |
w[], |
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double |
work[], |
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int |
lwork, |
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int * |
info |
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(Simple driver) Eigenvalues and eigenvectors of a symmetric matrix
- Purpose
- This routine computes all eigenvalues and, optionally, eigenvectors of a real symmetric matrix A. Eigenvalues and eigenvectors are computed by QL or QR method.
- Parameters
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| [in] | jobz | = 'N': Compute eigenvalues only.
= 'V': Compute eigenvalues and eigenvectors. |
| [in] | uplo | = 'U': Upper triangle of A is stored.
= 'L': Lower triangle of A is stored. |
| [in] | n | Order of the matrix A. (n >= 0) (If n = 0, returns without computation) |
| [in] | lda | Leading dimension of the two dimensional array a[][]. (lda >= max(1, n)) |
| [in,out] | a[][] | Array a[la][lda] (la >= n)
[in] The symmetric matrix A. If uplo = 'U', the leading n x n upper triangular part of a[][] contains the upper triangular part of the matrix A. If uplo = 'L', the leading n x n lower triangular part of a[][] contains the lower triangular part of the matrix A.
[out] jobz = 'V': If info = 0, a[][] contains the orthonormal eigenvectors of the matrix A.
jobz = 'N': The lower triangle (if uplo = 'L') or the upper triangle (if uplo = 'U') of a[][], including the diagonal, is destroyed. |
| [out] | w[] | Array w[lw] (lw >= n)
If info = 0, the eigenvalues in ascending order. |
| [out] | work[] | Array work[lwork]
Work array.
On exit, if info = 0, work[0] returns the optimal lwork. |
| [in] | lwork | The size of work[]. (lwork >= max(1, 3*n-1))
For optimal efficiency, lwork >= (nb + 2)*n, where nb is the optimal blocksize.
If lwork = -1, then a workspace query is assumed. The routine only calculates the optimal size of the work[] array, and returns the value in work[0]. |
| [out] | info | = 0: Successful exit.
= -1: The argument jobz had an illegal value. (jobz != 'V' nor 'N')
= -2: The argument uplo had an illegal value. (uplo != 'U' nor 'L')
= -3: The argument n had an illegal value. (n < 0)
= -4: The argument lda had an illegal value. (lda < max(1, n))
= -8: The argument lwork had an illegal value. (lwork too small)
= i > 0: The algorithm failed to converge; i off-diagonal elements of an intermediate tridiagonal form did not converge to zero. |
- Reference
- LAPACK
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1.9.6