poly2pwl.m

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function pwlcost = poly2pwl(polycost, Pmin, Pmax, npts)
%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.

%   MATPOWER Version 2.0
%   by Ray Zimmerman, PSERC Cornell    9/19/97
%   Copyright (c) 1997 by Power System Engineering Research Center (PSERC)
%   See http://www.pserc.cornell.edu/ for more info.

[PW_LINEAR, POLYNOMIAL, MODEL, STARTUP, SHUTDOWN, N, COST] = idx_cost;

pwlcost = polycost;
[m, n] = size(polycost);								%% size of piece being changed
pwlcost(:, MODEL) = PW_LINEAR * ones(m, 1);				%% change cost model
pwlcost(:, COST:n) = zeros(size(pwlcost(:, COST:n)));	%% zero out old data
pwlcost(:, N) = npts * ones(m, 1);						%% change number of data points

for i = 1:m
	if Pmin(i) == 0
		step = (Pmax(i) - Pmin(i)) / (npts - 1);
		xx = [Pmin(i):step:Pmax(i)];
	elseif Pmin(i) > 0
		step = (Pmax(i) - Pmin(i)) / (npts - 2);
		xx = [0 Pmin(i):step:Pmax(i)];
	elseif Pmin(i) < 0 & Pmax(i) > 0		%% for when P really means Q
		step = (Pmax(i) - Pmin(i)) / (npts - 1);
		xx = [Pmin(i):step:Pmax(i)];
	end
	yy = totcost(polycost(i, :), xx);
	pwlcost(i,		COST:2:(COST + 2*(npts-1)	 )) = xx;
	pwlcost(i,	(COST+1):2:(COST + 2*(npts-1) + 1)) = yy;
end

return;