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

Chapter 2 Basic Vector Operations 111
Euclidean norm squared SNRSQ/DNRSQ/SCNRSQ/DZNRSQ
INTEGER*8 n, incx
REAL*8 s, DZNRSQ
COMPLEX*16 x(lenx)
s = DZNRSQ(n, x, incx)
Input n Number of elements of vector x to be used in the
calculation. 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 square of the
Euclidean norm of x.
Fortran
Equivalent
REAL*4 FUNCTION SNRSQ (N, X,INCX)
REAL*4 X(*)
SNRSQ = 0.0
IF ( N .LE. 0 ) RETURN
IX = 1
INCXA = ABS ( INCX )
DO 10 I = 1, N
SNRSQ = SNRSQ + X(IX) ** 2
IX = IX + INCXA
10 CONTINUE
RETURN
END
Example Compute the square of the Euclidean norm of the REAL*8 vector x, where xis a
vector 10 elements long stored in a one-dimensional array X of dimension 20.
INTEGER*4 N,INCX
REAL*8 S,DNRSQ,X(20)
N = 10
INCX = 1
S = DNRSQ (N,X,INCX)