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

  sum                 real*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

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

  x                   real*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.

  incx                integer*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.