NAME

droti - Apply an indexed Givens rotation.

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

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

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

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