vec_dpostmult()

VEC_$DPOSTMULT                    Domain/OS                     VEC_$DPOSTMULT


NAME
     vec_$dpostmult - multiply a double-precision vector by a 4x4 matrix

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

     void vec_$dpostmult(
          double *matrix,
          double *start_vec,
          double *result_vec)

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

     procedure vec_$dpostmult(
          in matrix: univ vec_$double_matrix;
          in start_vec: univ vec_$double_vector;
          out result_vec: univ vec_$double_vector);

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

           double precision matrix(4, 4), start_vec(4), result_vec(4)

           call vec_$dpostmult(matrix, start_vec, result_vec)

DESCRIPTION
     Vec_$dpostmult multiplies the 4-element vector start_vec by the 4x4
     matrix matrix.

     In C, vec_$dpostmult applies matrix as a right transform to a row vector
     start_vec, and the resulting operation is

          for (j = 0; j < 4; ++j) {
               result_vec[j] = 0.0;
               for (i = 0; i < 4; ++i)
                    result_vec[j] += start_vec[i]
                                  * matrix[i][j];
          }

     In Pascal, vec_$dpostmult applies matrix as a right transform to a row
     vector start_vec, and the resulting operation is

          for j := 1 to 4 do
               begin
               result_vec[j] := 0.0;
               for i := 1 to 4 do
                    result_vec[j] := result_vec[j]
                                  + start_vec[i]
                                  * matrix[i,j];
               end

     In FORTRAN, vec_$dpostmult applies matrix as a left transform to a column
     vector start_vec, and the resulting operation is

           do 10 j = 1, 4
               result_vec(j) = 0.0
               do 10 i = 1, 4
                    result_vec(j) = result_vec(j)
          &                       + start_vec(i)
          &                       * matrix(j,i)
       10  continue

     matrix
          The matrix to multiply by start_vec.

     start_vec
          The vector to multiply by matrix.

     result_vec
          The product of start_vec and matrix.

NOTES
     Vec_$dpremult transforms double-precision vectors from the other side.

SEE ALSO
     vec_$ipostmult, vec_$ipostmult16, vec_$postmult.
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