vec_premultn()

VEC_$PREMULTN                     Domain/OS                      VEC_$PREMULTN


NAME
     vec_$premultn - multiply a single-precision vector by a matrix

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

     void vec_$premultn(
          float *start_vec,
          float *matrix,
          long int &m,
          long int &n,
          float *result_vec)

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

     procedure vec_$premultn(
          in start_vec: univ vec_$real_vector;
          in matrix: univ vec_$real_matrix;
          in m: integer32;
          in n: integer32;
          out result_vec: univ vec_$real_vector);

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

           integer*4 m, n
           parameter (m = 3, n = 4)

           real start_vec(m), matrix(m, n), result_vec(n)

           call vec_$premultn(start_vec, matrix, m, n, result_vec)

DESCRIPTION
     Vec_$premultn multiplies the m-element vector start_vec by the variably
     dimenstioned matrix matrix, and supplies the resulting n-element vector
     in result_vec.

     In C, vec_$premultn applies the nxm matrix matrix as a left transform to
     the m-element column vector start_vec, and supplies the transformed n-
     element result in result_vec:

          for (i = 0; i < n; ++i) {
               result_vec[i] = 0.0;
               for (j = 0; i < m; ++i)
                    result_vec[i] += start_vec[j]
                                  * matrix[i][j];
          }

     In Pascal, vec_$premultn applies the nxm matrix matrix as a left
     transform to the m-element column vector start_vec, and supplies the
     transformed n-element result in result_vec:

          for i := 1 to n do
               begin
               result_vec[i] := 0.0;
               for j := 1 to m do
                    result_vec[i] = result_vec[i]
                                  + start_vec[j]
                                  * matrix[i,j];
               end

     In FORTRAN, vec_$premultn applies the mxn matrix matrix as a right
     transform to the m-element row vector start_vec, and supplies the
     transformed n-element result in result_vec:

           do 10 i = 1, n
               result_vec(i) = 0.0
               do 10 j = 1, m
                    result_vec(i) = result_vec(i)
          &                       + start_vec(j)
          &                       * matrix(j,i)
       10  continue

     start_vec
          An m-element vector to multiply by matrix.

     matrix
          A matrix to multiply start_vec by.

     m    The number of elements in start_vec.

     n    The number of elements in result_vec.

     result_vec
          An n-element vector that is the product of matrix and start_vec.

NOTES
     Vec_$postmultn transforms single-precision vectors from the other side.

SEE ALSO
     vec_$dpremultn, vec_$ipremultn, vec_$ipremultn16.
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