Swap two vectors

 

 

SSWAP/DSWAP/ISWAP/CSWAP/ZSWAP

 

incx

Increment for the array x, incx ≠ 0:

 

 

incx > 0

x is stored forward in array x; that is,

 

 

 

xi is stored in x((i−1)⋅incx+1).

 

 

incx < 0

x is stored backward in array x; that

 

 

 

is, xi is stored in x((i−n)⋅incx+1).

 

 

Use incx = 1 if the vector x is stored contiguously in

 

 

array x; that is, if xi is stored in x(i). Refer to “BLAS

 

 

Indexing Conventions” in the introduction to this

 

 

chapter.

 

 

y

Array of length leny = (n−1)⋅incy+1 containing the

 

 

n-vector y.

 

 

incy

Increment for the array y, incy ≠ 0:

 

 

incy > 0

y is stored forward in array y; that is,

 

 

 

yi is stored in y((i−1)⋅incy+1).

 

 

incy < 0

y is stored backward in array y; that

 

 

 

is, yi is stored in y((i−n)⋅incy+1).

 

 

Use incy = 1 if the vector y is stored contiguously in

 

 

array y; that is, if yi is stored in y(i). Refer to “BLAS

 

 

Indexing Conventions” in the introduction to this

 

 

chapter.

 

Output

x and y

If n ≤ 0, then x and y are unchanged. Otherwise, x and

 

 

y are interchanged in x and y.

Notes

The result is unspecified if incx = 0 or incy = 0 or if x and y overlap such that

 

any element of x shares a memory location with any element of y.

Fortran

SUBROUTINE SSWAP (N, X,INCX, Y,INCY)

Equivalent

REAL*4 TEMP,X(*),Y(*)

 

IF ( N .LE. 0 ) RETURN

 

IX = 1

 

IY = 1

 

IF ( INCX .LT. 0 ) IX = 1 - (N-1) * INCX

 

IF ( INCY .LT. 0 ) IY = 1 - (N-1) * INCY

 

DO 10 I = 1, N

 

TEMP = X(IX)

 

X(IX) = Y(IY)

 

Y(IY) = TEMP

 

IX = IX + INCX

 

IY = IY + INCY

 

10 CONTINUE

 

RETURN

 

END

Chapter 2 Basic Vector Operations 143