{S,D}ASUM (n, x, incx) SCASUM (n, x, incx) DZASUM (n, x, incx)
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.
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 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|). On exit, incx is unchanged.
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.
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.