droti

NAME

droti, sroti - Apply a Givens rotation to x and y

SYNOPSIS

  SUBROUTINE DROTI( NZ, X, INDX, Y, C, S)
  INTEGER NZ
  INTEGER INDX(*)
  DOUBLE PRECISION C, S
  DOUBLE PRECISION X(*), Y(*)
 
  SUBROUTINE DROTI_64( NZ, X, INDX, Y, C, S)
  INTEGER*8 NZ
  INTEGER*8 INDX(*)
  DOUBLE PRECISION C, S
  DOUBLE PRECISION X(*), Y(*)

F95 INTERFACE

  SUBROUTINE ROTI( [NZ], X, INDX, Y, C, S)
  INTEGER :: NZ
  INTEGER, DIMENSION(:) :: INDX
  REAL(8) :: C, S
  REAL(8), DIMENSION(:) :: X, Y
 
  SUBROUTINE ROTI_64( [NZ], X, INDX, Y, C, S)
  INTEGER(8) :: NZ
  INTEGER(8), DIMENSION(:) :: INDX
  REAL(8) :: C, S
  REAL(8), DIMENSION(:) :: X, Y

PURPOSE

droti xROTI - Applies a Givens rotation to a sparse vector x stored in compressed form and another vector y in full storage form

             do 10, i = 1, n
               temp = -s * x(i) + c * y(indx(i))
               x(i) = c * x(i) + s * y(indx(i))
               y(indx(i)) = temp
          10 continue

ARGUMENTS

* NZ (input)

- INTEGER

Number of elements in the compressed form. Unchanged on exit.

* X (input)

Vector containing the values of the compressed form.

* INDX (input)

- INTEGER

Vector containing the indices of the compressed form. It is assumed that the elements in INDX are distinct and greater than zero. Unchanged on exit.

* Y (input/output)

Vector on input which contains the vector Y in full storage form. On exit, only the elements corresponding to the indices in INDX have been modified.

* C (input)

Scalar defining the Givens rotation

* S (input)

Scalar defining the Givens rotation