poly2pwl

POLY2PWL  Converts polynomial cost variable to piecewise linear.
   PWLCOST = POLY2PWL(POLYCOST, PMIN, PMAX, NPTS) converts the polynomial
   cost variable POLYCOST into a piece-wise linear cost by evaluating at
   zero and then at NPTS evenly spaced points between PMIN and PMAX. If
   PMIN <= 0 (such as for reactive power, where P really means Q) it just
   uses NPTS evenly spaced points between PMIN and PMAX.

0001 function pwlcost = poly2pwl(polycost, Pmin, Pmax, npts)
0002 %POLY2PWL  Converts polynomial cost variable to piecewise linear.
0003 %   PWLCOST = POLY2PWL(POLYCOST, PMIN, PMAX, NPTS) converts the polynomial
0004 %   cost variable POLYCOST into a piece-wise linear cost by evaluating at
0005 %   zero and then at NPTS evenly spaced points between PMIN and PMAX. If
0006 %   PMIN <= 0 (such as for reactive power, where P really means Q) it just
0007 %   uses NPTS evenly spaced points between PMIN and PMAX.
0008 
0009 %   MATPOWER
0010 %   $Id: poly2pwl.m 1635 2010-04-26 19:45:26Z ray $
0011 %   by Ray Zimmerman, PSERC Cornell
0012 %   Copyright (c) 1996-2010 by Power System Engineering Research Center (PSERC)
0013 %
0014 %   This file is part of MATPOWER.
0015 %   See http://www.pserc.cornell.edu/matpower/ for more info.
0016 %
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0037 
0038 [PW_LINEAR, POLYNOMIAL, MODEL, STARTUP, SHUTDOWN, NCOST, COST] = idx_cost;
0039 
0040 pwlcost = polycost;
0041 [m, n] = size(polycost);                                %% size of piece being changed
0042 pwlcost(:, MODEL)  = PW_LINEAR * ones(m, 1);            %% change cost model
0043 pwlcost(:, COST:n) = zeros(size(pwlcost(:, COST:n)));   %% zero out old data
0044 pwlcost(:, NCOST)  = npts * ones(m, 1);                 %% change number of data points
0045 
0046 for i = 1:m
0047     if Pmin(i) == 0
0048         step = (Pmax(i) - Pmin(i)) / (npts - 1);
0049         xx = (Pmin(i):step:Pmax(i));
0050     elseif Pmin(i) > 0
0051         step = (Pmax(i) - Pmin(i)) / (npts - 2);
0052         xx = [0 Pmin(i):step:Pmax(i)];
0053     elseif Pmin(i) < 0 && Pmax(i) > 0        %% for when P really means Q
0054         step = (Pmax(i) - Pmin(i)) / (npts - 1);
0055         xx = (Pmin(i):step:Pmax(i));
0056     end
0057     yy = totcost(polycost(i, :), xx);
0058     pwlcost(i,      COST:2:(COST + 2*(npts-1)    )) = xx;
0059     pwlcost(i,  (COST+1):2:(COST + 2*(npts-1) + 1)) = yy;
0060 end