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## org.netlib.lapack
Class Dsytf2

    java.lang.Object
      org.netlib.lapack.Dsytf2

    public class Dsytf2

extends java.lang.Object

    Following is the description from the original
    Fortran source.  For each array argument, the Java
    version will include an integer offset parameter, so
    the arguments may not match the description exactly.
    Contact seymour@cs.utk.edu with any questions.

     *     ..
     *
     *  Purpose
     *  =======
     *
     *  DSYTF2 computes the factorization of a real symmetric matrix A using

     *  the Bunch-Kaufman diagonal pivoting method:
     *
     *     A = U*D*U'  or  A = L*D*L'
     *
     *  where U (or L) is a product of permutation and unit upper (lower)
     *  triangular matrices, U' is the transpose of U, and D is symmetric and
     *  block diagonal with 1-by-1 and 2-by-2 diagonal blocks.
     *
     *  This is the unblocked version of the algorithm, calling Level 2 BLAS.
     *
     *  Arguments
     *  =========
     *
     *  UPLO    (input) CHARACTER*1
     *          Specifies whether the upper or lower triangular part of the
     *          symmetric matrix A is stored:
     *          = 'U':  Upper triangular
     *          = 'L':  Lower triangular
     *
     *  N       (input) INTEGER
     *          The order of the matrix A.  N >= 0.
     *
     *  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
     *          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
     *          n-by-n upper triangular part of A contains the upper
     *          triangular part of the matrix A, and the strictly lower
     *          triangular part of A is not referenced.  If UPLO = 'L', the
     *          leading n-by-n lower triangular part of A contains the lower

     *          triangular part of the matrix A, and the strictly upper
     *          triangular part of A is not referenced.
     *
     *          On exit, the block diagonal matrix D and the multipliers used
     *          to obtain the factor U or L (see below for further details).

     *
     *  LDA     (input) INTEGER
     *          The leading dimension of the array A.  LDA >= max(1,N).
     *
     *  IPIV    (output) INTEGER array, dimension (N)
     *          Details of the interchanges and the block structure of D.
     *          If IPIV(k) > 0, then rows and columns k and IPIV(k) were
     *          interchanged and D(k,k) is a 1-by-1 diagonal block.
     *          If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and
     *          columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k)
     *          is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) =
     *          IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were
     *          interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.
     *
     *  INFO    (output) INTEGER
     *          = 0: successful exit
     *          < 0: if INFO = -k, the k-th argument had an illegal value
     *          > 0: if INFO = k, D(k,k) is exactly zero.  The factorization

     *               has been completed, but the block diagonal matrix D is
     *               exactly singular, and division by zero will occur if it

     *               is used to solve a system of equations.
     *
     *  Further Details
     *  ===============
     *
     *  09-29-06 - patch from
     *    Bobby Cheng, MathWorks
     *
     *    Replace l.204 and l.372
     *         IF( MAX( ABSAKK, COLMAX ).EQ.ZERO ) THEN
     *    by
     *         IF( (MAX( ABSAKK, COLMAX ).EQ.ZERO) .OR. DISNAN(ABSAKK) ) THEN
     *
     *  01-01-96 - Based on modifications by
     *    J. Lewis, Boeing Computer Services Company
     *    A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA

     *  1-96 - Based on modifications by J. Lewis, Boeing Computer Services
     *         Company
     *
     *  If UPLO = 'U', then A = U*D*U', where
     *     U = P(n)*U(n)* ... *P(k)U(k)* ...,
     *  i.e., U is a product of terms P(k)*U(k), where k decreases from n to

     *  1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
     *  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
     *  defined by IPIV(k), and U(k) is a unit upper triangular matrix, such

     *  that if the diagonal block D(k) is of order s (s = 1 or 2), then
     *
     *             (   I    v    0   )   k-s
     *     U(k) =  (   0    I    0   )   s
     *             (   0    0    I   )   n-k
     *                k-s   s   n-k
     *
     *  If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k).
     *  If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k),
     *  and A(k,k), and v overwrites A(1:k-2,k-1:k).
     *
     *  If UPLO = 'L', then A = L*D*L', where
     *     L = P(1)*L(1)* ... *P(k)*L(k)* ...,
     *  i.e., L is a product of terms P(k)*L(k), where k increases from 1 to

     *  n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1
     *  and 2-by-2 diagonal blocks D(k).  P(k) is a permutation matrix as
     *  defined by IPIV(k), and L(k) is a unit lower triangular matrix, such

     *  that if the diagonal block D(k) is of order s (s = 1 or 2), then
     *
     *             (   I    0     0   )  k-1
     *     L(k) =  (   0    I     0   )  s
     *             (   0    v     I   )  n-k-s+1
     *                k-1   s  n-k-s+1
     *
     *  If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k).
     *  If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k),
     *  and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1).
     *
     *  =====================================================================
     *
     *     .. Parameters ..

Constructor Summary
`Dsytf2()`

Method Summary
`static void` | `dsytf2(java.lang.String uplo, int n, double[] a, int _a_offset, int lda, int[] ipiv, int _ipiv_offset, intW info)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### Dsytf2

    public Dsytf2()

Method Detail

### dsytf2

    public static void dsytf2(java.lang.String uplo,
                              int n,
                              double[] a,
                              int _a_offset,
                              int lda,
                              int[] ipiv,
                              int _ipiv_offset,
                              intW info)

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