HP MLIB User's Guide Vol. 1 7th Ed.

108 HP MLIB User’s Guide
SNRM2/DNRM2/SCNRM2/DZNRM2 Euclidean norm
INTEGER*8 n, incx
REAL*8 s, DZNRM2
COMPLEX*16 x(lenx)
s = DZNRM2(n, x, incx)
Input n Number of elements of vector x to be used in the
Euclidean norm. If n ≤ 0, the subprograms do not
reference x.
x Array of length lenx = (n−1)×|incx|+1 containing the
n-vector x.
incx Increment for the array x. x is stored forward in array x
with increment |incx|; that is, x
i
is stored in
x((i−1)×|incx|+1).
Use incx = 1 if the vector x is stored contiguously in
array x; that is, if x
i
is stored in x(i). Refer to “BLAS
Indexing Conventions” in the introduction to this
chapter.
Output s If n ≤ 0, then s = 0. Otherwise, s is the Euclidean norm
of x.
Fortran
Equivalent
REAL*4 FUNCTION SNRM2 ( N, X,INCX )
INTEGER*4 INCX, INCXA, IX, N
REAL*4 ABSXI, SCALE, SSQ, X(*)
IF ( N .GT. 1 ) THEN
INCXA = ABS ( INCX )
SCALE = 0.0
SSQ = 1.0
DO 10 IX = 1, 1 + (N-1)*INCXA, INCXA
IF ( X(IX) .NE.0.0 ) THEN
ABSXI = ABS ( X(IX) )
IF ( SCALE .LT. ABSXI ) THEN
SSQ = 1.0 + SSQ * (SCALE/ABSXI) ** 2
SCALE = ABSXI
ELSE
SSQ = SSQ + (ABSXI/SCALE) ** 2
END IF
END IF
10 CONTINUE
SNRM2 = SCALE * SQRT ( SSQ )
ELSE IF ( N .EQ. 1 ) THEN
SNRM2 = ABS ( X(1) )
ELSE
SNRM2 = 0.0
END IF
RETURN
END