VEC_$IREC216                      Domain/OS                       VEC_$IREC216


NAME
     vec_$irec216 - calculate second-order linear recurrence of integer vector

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

     void vec_$irec216(
          short int *start_vec,
          short int *vec_2,
          short int *vec_3,
          long int &count,
          short int *result_vec)

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

     procedure vec_$irec216(
          in start_vec: univ vec_$integer16_vector;
          in vec_2: univ vec_$integer16_vector;
          in vec_3: univ vec_$integer16_vector;
          in count: integer32;
          var result_vec: univ vec_$integer16_vector);

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

           parameter (nvec = 10)

           integer*2 start_vec(nvec), result_vec(nvec), vec_2(nvec), vec_3(nvec)
           integer*4 count

           call vec_$irec216(start_vec, vec_2, vec_3, count, result_vec)

DESCRIPTION
     Vec_$irec216 calculates a second-order linear recurrence based on
     start_vec, vec_2, and vec_3.  It differs from vec_$rec2 in that the vec-
     tors being handled contain short integers.

     This routine reads the first and second entries in the array result_vec;
     it then writes count entries into result_vec based on the following for-
     mula:

     For each integer I such that 1 <= I <= count,
     result_vec(I+2) = start_vec(I) + (vec_2(I) x result_vec(I+1))
                        + (vec_3(I) x result_vec(I))

     Notice that result_vec is used both for input and output, and that it
     must be large enough to hold count + 2 entries.

     start_vec
          An input vector.

     vec_2
          An input vector.

     vec_3
          An input vector.

     count
          The number of elements to be operated on.

     result_vec
          The vector containing two input variables and the output from the
          recurrence calculations.

NOTES
     When vec_$irec216 is used to operate on matrixes in C and Pascal,
     start_vec, vec_2, vec_3, and result_vec are row vectors; in FORTRAN, they
     are column vectors.

     As in all the vec_$ calls,  the result array must not overlap any of the
     input arrays; the result array may be identical to an input, but must not
     contain any smaller subset of an input.   Because of pipelining, using
     overlapping input and output arrays may cause incorrect results.

     vec_$irec216, like all 16-bit integer routines, performs poorly when com-
     pared to the 32-bit integer routines.  Its use should be avoided wherever
     possible, especially on high-performance workstations.

SEE ALSO
     vec_$rec2, vec_$rec2c, vec_$rec2_i, vec_$drec2, vec_$drec2_i, vec_$irec2,
     vec_$irec2_i, vec_$irec216_i.