Name

sasum, dasum, scasum, dzasum − Sum of the absolute value

FORMAT

{S,D}ASUM (n, x, incx) SCASUM (n, x, incx) DZASUM (n, x, incx)

Function Value

sum: real∗4 | real∗8 | complex∗8 | complex∗16
The sum of the absolute values of the elements of the vector x.
If n<=0, sum returns the value 0.0.

Arguments

ninteger∗4
On entry, the number of elements in the vector x.
On exit, n is unchanged.

xreal∗4 | real∗8 | complex∗8 | complex∗16
On entry, a one-dimensional array X of length at least (1+(n-1)∗|incx|), containing the elements of the vector x.
On exit, x is unchanged.

incxinteger∗4
On entry, the increment for the array X.
If incx >= 0, vector x is stored forward in the array, so that x(i) is stored in location X(1+(i-1)∗incx).
If incx < 0, vector x is stored backward in the array, so that x(i) is stored in location X(1+(n-i)∗|incx|).
On exit, incx is unchanged.

Description

The SASUM and DASUM functions compute the sum of the absolute values of the elements of a real vector x: SUM(i=1...n,|x(i)|) = |x(1)| + |x(2)| + ... + |x(n)|

SCASUM and DZASUM compute the sum of the absolute values of the real and imaginary parts of the elements of a complex vector x: SUM(i=1...(n),|a(i)| + |b(i)|) = (|a(1)| + |b(1)|) + (|a(2)| + |b(2)|) + ...  + (|a(n)| + |b(n)|)

where x(i) = (a(i),b(i)) and |x(i)| = |a(i)| + |b(i)| = |real| + |imaginary|

If incx < 0, the result is identical to using |incx|.  If (incx = 0, the computation is a time-consuming way of setting sum = n∗x(1). 

Because of the efficient coding of these routines, rounding errors can cause the final result to differ from the result computed by a sequential evaluation of the sum of the elements of the vector. 

Example

INTEGER∗4 N, INCX
REAL∗4 X(20), SUM
INCX = 1
N = 20
SUM = SASUM(N,X,INCX)

This FORTRAN code shows how to compute the sum of the absolute values of the elements of the vector x.