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VEC_$DREC2C_I                     Domain/OS                      VEC_$DREC2C_I


NAME
     vec_$drec2c_i - calculate second-order linear recurrence of double-
     precision vector with constant coefficients

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

     void vec_$drec2c_i(
          double *start_vec,
          long int &start_inc,
          long int &count,
          double &mult_constant,
          double &mult_constant_2,
          double *result_vec,
          long int &result_inc)

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

     procedure vec_$drec2c_i(
          in start_vec: univ vec_$double_vector;
          in start_inc: integer32;
          in count: integer32;
          in mult_constant: double;
          in mult_constant_2: double;
          var result_vec: univ vec_$double_vector;
          in result_inc: integer32);

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

           parameter (nvec = 10)

           real*8 start_vec(nvec), result_vec(nvec), mult_constant, mult_constant_2
           integer*4 count
           integer*4 start_inc, result_inc

           call vec_$drec2c_i(start_vec, start_inc, count,
          & mult_constant, mult_constant_2, result_vec, result_inc)

DESCRIPTION
     Vec_$drec2c_i calculates a second-order linear recurrence with constant
     coefficients based on start_vec.  It differs from vec_$rec2c_i in that
     the vectors being handled are double-precision floating point.

     This call, like all vec_$ calls ending in _i, takes a set of extra stride
     arguments, one for every vector argument.  The stride arguments determine
     which elements in the array are actually processed.  For instance, if the
     stride for a particular array is set to 3, every third element in the
     array will be processed by the routine.  The stride arguments need not be
     identical.  If all stride arguments are set to 1, this call behaves
     exactly like the version without the _i in its name.

     This routine reads the first two entries in the array result_vec; it then
     writes count entries into result_vec based on the following formula:

     Initialize the counter variables J and K to the low indices of the arrays
     start_vec and result_vec.  In Fortran, the low index will be 1;  in C, it
     will be 0; in Pascal, it varies depending on the declaration.
     Execute the following equations count times:
     result_vec(K+2) = start_vec(J) + (mult_constant x result_vec(K+1))
                        + (mult_constant_2 x result_vec(K))
     J = J + start_inc
     K = K + result_inc

     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.

     start_inc
          The stride for start_vec.

     mult_constant
          A scalar multiplier.

     mult_constant_2
          A scalar multiplier.

     count
          The number of elements to be operated on.

     result_vec
          The vector containing two input values and the result of the
          recurrence calculation.

     result_inc
          The stride for result_vec.

NOTES
     When vec_$drec2c_i is used to operate on matrixes in C and Pascal,
     start_vec 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.


SEE ALSO
     vec_$rec2, vec_$rec2c, vec_$rec2c_i, vec_$drec2c, vec_$irec2c,
     vec_$irec2c_i, vec_$irec2c16, vec_$irec2c16_i.