Extract fractional parts

 

SFRAC/DFRAC

 

 

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

y

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

 

 

n-vector y. If n ≤ 0, y is unchanged. Otherwise, yi is the

 

 

fractional part of xi.

Notes

The fractional part of a number is either zero or of the same sign as the number.

Thus, the fractional parts of −1.4, −1.0, 0.6, and 2.0 are −0.4, 0.0, 0.6, and 0.0, respectively. x and y can be the same array if incx = incy. Otherwise, the result is unspecified if x and y overlap such that any element of x shares a memory location with any element of y.

Fortran Equivalent

SUBROUTINE SFRAC (N, X,INCX, Y,INCY) REAL*4 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

Y(IY) = X(IX) - AINT ( X(IX) ) IX = IX + INCX

IY = IY + INCY

10CONTINUE RETURN END

Example Extract the fractional parts of the elements of the REAL*8 vector x into y, where x and y are vectors 10 elements long stored in one-dimensional arrays X and Y of dimension 20.

INTEGER*4 N,INCX,INCY

REAL*8

X(20),Y(20)

N = 10

 

INCX = 1

 

INCY

= 1

 

CALL

DFRAC (N,X,INCX,Y,INCY)

Chapter 2 Basic Vector Operations 93