# ?roti

Applies Givens rotation to sparse vectors one of which is in compressed form.

## Syntax

FORTRAN 77:

call sroti(nz, x, indx, y, c, s)

call droti(nz, x, indx, y, c, s)

Fortran 95:

call roti(x, indx, y [, c] [,s])

## Description

The ?roti routines apply the Givens rotation to elements of two real vectors, x (in compressed form nz, x, indx) and y (in full storage form):

x(i) = c*x(i) + s*y(indx(i))

y(indx(i)) = c*y(indx(i))- s*x(i)

The routines reference only the elements of y whose indices are listed in the array indx. The values in indx must be distinct.

## Input Parameters

nz

  INTEGER. The number of elements in x and indx.

x

  REAL for sroti

  DOUBLE PRECISION for droti

  Array, DIMENSION at least nz.

indx

  INTEGER. Specifies the indices for the elements of x.

  Array, DIMENSION at least nz.

y

  REAL for sroti

  DOUBLE PRECISION for droti

  Array, DIMENSION at least max(indx(i)).

c

  A scalar: REAL for sroti

  DOUBLE PRECISION for droti.

s

  A scalar: REAL for sroti

  DOUBLE PRECISION for droti.

## Output Parameters

x and y

  The updated arrays.

## Fortran 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see Fortran 95 Interface Conventions.

Specific details for the routine roti interface are the following:

x

  Holds the vector of length (nz).

indx

  Holds the vector of length (nz).

y

  Holds the vector of length (nz).

c

  The default value is 1.

s

  The default value is 1.

Parent topic: Sparse BLAS Level 1 Routines