vec_dsum_i() — Apollo

VEC_$DSUM_I                       Domain/OS                        VEC_$DSUM_I


NAME
     vec_$dsum_i - sum the elements of a vector in a double-precision matrix

SYNOPSIS (C)
     #include <apollo/base.h>
     #include <apollo/vec.h>

     double vec_$dsum_i(
          double *vec,
          long int &inc,
          long int &length)

SYNOPSIS (Pascal)
     %include '/sys/ins/base.ins.pas';
     %include '/sys/ins/vec.ins.pas';

     function vec_$dsum_i(
          in vec: univ vec_$double_vector;
          in inc: integer32;
          in length: integer32): double;

SYNOPSIS (FORTRAN)
     %include '/sys/ins/base.ins.ftn'
     %include '/sys/ins/vec.ins.ftn'

           parameter (nvec = 10)

           double precision vec(nvec), sum
           integer*4 length, inc

           sum = vec_$sum_i(vec, inc, length)

DESCRIPTION
     Vec_$dsum_i adds length elements from the double-precision array vector
     selected by inc and returns the sum.

     Through appropriate choice of inc, a program can use vec_$dsum_i to sum
     an individual vector in a matrix.  To sum the Mth vector in a matrix
     choose inc equal to the number of vectors in the matrix.

     In C, the resulting operation is

          return_value = 0.0;
          j = 0;
          for (i = 0; i < length; ++i) {
               return_value += vec[j];
               j += inc;
          }

     In Pascal, the resulting operation is

          return_value := 0.0;
          j := 1;
          for i := 1 to length do
               begin
               return_value := return_value + vec[j];
               j := j + inc;
               end

     In FORTRAN, the resulting operation is

           vec_$dsum_i = 0.0
           j = 1
           do 10 i = 1, length
               vec_$dsum_i = vec_$dsum_i + vec(j)
               j = j + inc
       10  continue

     vec  An array that contains the elements to sum.

     inc  An increment for the index of vec that selects which elements of vec
          are summed.

     length
          The number of elements in vec to sum.

NOTES
     In C and Pascal, vec_$dsum_i sums a column vector; whereas in FORTRAN, it
     sums a row vector.

SEE ALSO
     vec_$dsum, vec_$isum16_i, vec_$isum_i, vec_$sum_i.
Museum
