dsptrd (l) - Linux Manuals

dsptrd: reduces a real symmetric matrix A stored in packed form to symmetric tridiagonal form T by an orthogonal similarity transformation

NAME

DSPTRD - reduces a real symmetric matrix A stored in packed form to symmetric tridiagonal form T by an orthogonal similarity transformation

SYNOPSIS

SUBROUTINE DSPTRD(
UPLO, N, AP, D, E, TAU, INFO )

    
CHARACTER UPLO

    
INTEGER INFO, N

    
DOUBLE PRECISION AP( * ), D( * ), E( * ), TAU( * )

PURPOSE

DSPTRD reduces a real symmetric matrix A stored in packed form to symmetric tridiagonal form T by an orthogonal similarity transformation: Q**T * A * Q = T.

ARGUMENTS

UPLO (input) CHARACTER*1
= aqUaq: Upper triangle of A is stored;
= aqLaq: Lower triangle of A is stored.
N (input) INTEGER
The order of the matrix A. N >= 0.
AP (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
On entry, the upper or lower triangle of the symmetric matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = aqUaq, AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = aqLaq, AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n. On exit, if UPLO = aqUaq, the diagonal and first superdiagonal of A are overwritten by the corresponding elements of the tridiagonal matrix T, and the elements above the first superdiagonal, with the array TAU, represent the orthogonal matrix Q as a product of elementary reflectors; if UPLO = aqLaq, the diagonal and first subdiagonal of A are over- written by the corresponding elements of the tridiagonal matrix T, and the elements below the first subdiagonal, with the array TAU, represent the orthogonal matrix Q as a product of elementary reflectors. See Further Details. D (output) DOUBLE PRECISION array, dimension (N) The diagonal elements of the tridiagonal matrix T: D(i) = A(i,i).
E (output) DOUBLE PRECISION array, dimension (N-1)
The off-diagonal elements of the tridiagonal matrix T: E(i) = A(i,i+1) if UPLO = aqUaq, E(i) = A(i+1,i) if UPLO = aqLaq.
TAU (output) DOUBLE PRECISION array, dimension (N-1)
The scalar factors of the elementary reflectors (see Further Details).
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value

FURTHER DETAILS

If UPLO = aqUaq, the matrix Q is represented as a product of elementary reflectors

Q = H(n-1) . . . H(2) H(1).
Each H(i) has the form

H(i) = I - tau * v * vaq
where tau is a real scalar, and v is a real vector with
v(i+1:n) = 0 and v(i) = 1; v(1:i-1) is stored on exit in AP, overwriting A(1:i-1,i+1), and tau is stored in TAU(i).
If UPLO = aqLaq, the matrix Q is represented as a product of elementary reflectors

Q = H(1) H(2) . . . H(n-1).
Each H(i) has the form

H(i) = I - tau * v * vaq
where tau is a real scalar, and v is a real vector with
v(1:i) = 0 and v(i+1) = 1; v(i+2:n) is stored on exit in AP, overwriting A(i+2:n,i), and tau is stored in TAU(i).

Pages related to dsptrd

  • dsptrd (3)
  • dsptrf (l) - computes the factorization of a real symmetric matrix A stored in packed format using the Bunch-Kaufman diagonal pivoting method
  • dsptri (l) - computes the inverse of a real symmetric indefinite matrix A in packed storage using the factorization A = U*D*U**T or A = L*D*L**T computed by DSPTRF
  • dsptrs (l) - solves a system of linear equations A*X = B with a real symmetric matrix A stored in packed format using the factorization A = U*D*U**T or A = L*D*L**T computed by DSPTRF
  • dspcon (l) - estimates the reciprocal of the condition number (in the 1-norm) of a real symmetric packed matrix A using the factorization A = U*D*U**T or A = L*D*L**T computed by DSPTRF
  • dspev (l) - computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage
  • dspevd (l) - computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage
  • dspevx (l) - computes selected eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage