get_color_grade(densities, flows, celldata, a)

function clrs = get_color_grade(densities, flows, celldata, a)
% GET_COLOR_GRADE - returns array of colors that corresponds to the array of
%                   densities: green means free flow, red means congested.
%
% Call:
%       clrs = get_color_grade(densities, flows, celldata)
%       clrs = get_color_grade(densities, flows, celldata, a)
%
% Parameters:
%             densities - vector of density values;
%             flows     - vector of flows, must be the same size as 'densities';
%             celldata  - array of freeway cell structures, whose length must be
%                         the same as size of 'densities' and 'flows';
%             a         - fraction of maximum flow used to determine
%                         yellow and orange colors (this parameter is optional,
%                         default value is 0.95).
%
% Returns:   clrs - vertical array of colors.
%
% Last modified:   07/30/2006.

%
% Alex Kurzhanskiy   <[e-mail]>
%

G = [0 1 0];  % green
Y = [1 1 0];  % yellow
O = [1 0.4 0.07];  % orange
R = [0.8 0 0];  % red

if nargin < 4
  c = [0.95 0.95];  % default: 95% of maximum flow
else
  c = [a a];
end

m = size(densities, 1);
n = size(celldata, 2);
if m ~= n
  error('GET_COLOR_GRADE: number of densities does not match number of cells.');
end

clrs = [];

for i = 1:n
  if densities(i, 1) <= celldata(i).FDrhocrit
    if flows(i, 1) <= (c(1) * celldata(i).FDfmax)
      clrs = [clrs; G];  % free flow
    else
      clrs = [clrs; Y];  % free flow, but reaching more than 95% maximum capacity
    end
  else
    if flows(i, 1) <= (c(2) * celldata(i).FDfmax)
      clrs = [clrs; R];  % congested
    else
      clrs = [clrs; O];  % congested, but reaching more than 95% maximum capacity
    end
  end
end

return;