Function            double_decline_bal_dep - calculate double
                                                 declining balance
                                                 depreciation

  Syntax              double double_decline_bal_dep(double cost, int
                                                    life, int period);

  Prototype in        finance.h

  Remarks             given the cost and life of an item,
                      double_decline_bal_dep will calculate the amount of
                      deprecitation for the given period according to the
                      double declining balance depreciation method. The
                      cost can be given in any unit (dollars, thousands
                      of dollars, etc.) but the life should be given in
                      depreciable periods (if you depreciate an item
                      every quarter, and the item has a life of 2 years,
                      then life should be 8).

                      The life and period should be given in the same
                      units.

                      No error checking is performed.

  Return value        returns the amount of depreciation for the given
                      period in the same units as the cost, as per the
                      double declining balance depreciation method.

  Note                The macro DDB(c,l,p) is defined in finance.h for
                      ease of use.

  See also            accum_dep(), depreciation(), straight_line_dep(),
                      sum_year_digits_dep()

  Example             see demonum.c