Name

ssum, dsum, csum, zsum − Sum of the values of the elements of a vector

FORMAT

{S,D,C,Z}SUM (n, x, incx)

Function Value

sumreal∗4 | real∗8 | complex∗8 | complex∗16
The total of the values of the elements in 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 n 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|). 
If incx = 0, only the first element is accessed. 
On exit, incx is unchanged. 

Description

The _SUM subprograms compute the total value of the elements of a vector, performing the following operation: SUM(i=1...n,x(i))
Because of efficient coding, 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.

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

Example

INTEGER∗4 N, INCX
REAL∗4 X(200), SUM
INCX = 2
N = 50
SUM = SSUM(N,X,INCX)

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