MATLAB: Adjusting plot fill to show two colours depending on overestima​​tion/unde​r​estimati​on

fillgraphhandlespatchplot

Hello,
I have the following code to plot my observed readings versus my modelled readings and the code works fine but does not clearly show regions where my modelled data is greater than observed data.
% Create figure
figure1 = figure;
XData = mod1_2001_2014(x,1)'; 
YData1 = mod1_2001_2014(x,5)'; 
YData2 = mod1_2001_2014(x,4)';
% Plot with fill
X = [XData fliplr(XData)];
Y = [YData1 fliplr(YData2)];
fill(X,Y,[0.678431391716003 0.921568632125854 1]);
ylim([0 max(YData2)+3])
I was wondering if there is a way to have this so that when the YData2 > YData1 the fill is red and when YData1 > YData2, the fill is the colour it is now.
Any ideas? Thank you!

Best Answer

Have a look at http://www.mathworks.com/matlabcentral/fileexchange/34876--greater-than--fill
or my solution that does need no interpolation but computes the intersection points.
function fillline(x, y1, y2, col1, col2) 
% Thorsten Hansen 2015-05-02 2014-11-27
% See also
% http://www.mathworks.com/matlabcentral/fileexchange/34876--greater-than--fill
if nargin < 3
  x = -10:10;
  y1 = sin(x);
  y2 = cos(x);
end
if nargin < 5
  col1 = [1 0 0];
  col2 = [0 0 1];
end
hold on
colpatch(y1 >= y2, col1, x, y1, y2)
colpatch(y2 >= y1, col2, x, y1, y2)
plot(x, y1, '-', 'Color', col1)
plot(x, y2, '-', 'Color', col2)
hold off
function colpatch(ind, col, x, y1, y2)
% special case 1: all values of y2 below y1: nothing to fill
if ~any(ind)
  return
end
% define fill color as a lighter version of the color on the line above
col = lighten(col);
% force row vectors for proper concatenation in fill below
x = x(:)'; y1 = y1(:)'; y2 = y2(:)'; ind = ind(:)';
% special case 2: no intersections, all values of y2 above y1
if all(ind)
  fill([x x(end) fliplr(x) x(1)], ...
       [y1 y1(end) fliplr(y2) y2(1)], col, 'EdgeColor', col);
  return
end
% general case: y1 and y2 intersect
val = cumsum(diff([0 ind]) == 1).*ind;
v = 1;
ind = find(val == v);
while ~isempty(ind)
  xi = x(ind); y1i = y1(ind); y2i = y2(ind); 
    % determine intersections to fill area between intersections
    % determine left intercept
    ii = ind(1);
    if ii > 1
      line1 = [x(ii) y1(ii); x(ii-1) y1(ii-1)];
      line2 = [x(ii) y2(ii); x(ii-1) y2(ii-1)];
      [xis_left yis_left] = lineintercept(line1, line2);
    else
      xis_left = [];
      yis_left = [];
    end
    % determine right intercept
    ii = ind(end);
    if ii < numel(x) 
      line1 = [x(ii) y1(ii); x(ii+1) y1(ii+1)];
      line2 = [x(ii) y2(ii); x(ii+1) y2(ii+1)];
      [xis_right yis_right] = lineintercept(line1, line2);
    else
      xis_right = [];
      yis_right = [];
    end
    % add patch
    fill([xis_left xi xis_right fliplr(xi)], ...
         [yis_left y1i yis_right fliplr(y2i)], col, 'EdgeColor', col);
    %set(h), pause
    v = v + 1; % next patch
    ind = find(val == v); % indices of next patch
  end
function [xis  yis] = lineintercept(line1, line2)
slope = @(line) (line(2,2) - line(1,2))/(line(2,1) - line(1,1));
m1 = slope(line1);
m2 = slope(line2);
intercept = @(line,m) line(1,2) - m*line(1,1);
b1 = intercept(line1,m1);
b2 = intercept(line2,m2);
% intersection
xis = (b2-b1)/(m1-m2);
yis = m1*xis + b1;
%plot(xis,yis,'ko','MarkerSize',10)
function col = lighten(col)
col = col + 0.8*([1 1 1] - col);
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