MATLAB Answers


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

Asked by mashtine on 27 Nov 2014
Latest activity Commented on by mashtine on 9 Feb 2015
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!


Sign in to comment.

2 Answers

Answer by Thorsten
on 27 Nov 2014
Edited by Thorsten
on 5 Feb 2015
 Accepted Answer

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
if nargin < 3
x = -10:10;
y1 = sin(x);
y2 = cos(x);
if nargin < 5
col1 = [1 0 0];
col2 = [0 0 1];
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)
% 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);
% 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);
xis_left = [];
yis_left = [];
% 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);
xis_right = [];
yis_right = [];
% 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
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;
function col = lighten(col)
col = col + 0.8*([1 1 1] - col);


Hi Thorsten,
Thanks again for this! Ran into another issue. When I reach to row 155 of my testdata (attached) the code goes wonky and I think it has to do with when y2 is greater than y1. It does not seem to be doing the switch even with both versions above. Unfortunately I am not too familiar with the colpatch function to figure it out myself.
Hi Masao,
I missed to also force "ind" to be a row vector. Please find the updated fillline function above. Hope this works now smoothly for everything :-)

Sign in to comment.

Answer by Luuk van Oosten on 27 Nov 2014

Dear Massao,
I do not know exactly how your data looks like, but you could use somthing like:
for i=1:lenght(yourdataset)
if YData1 < YData2 % Let matlab check if Ydata2 is larger than YData1
scatter( x(i,1), y(i,5), 15, [1 0 0], 'filled') hold on;
else % if this condition is not matched, then do the following:
scatter( x(i,1), y(i,4),15, [0 0.68 0.92], 'filled') hold on;
Have fun!


Hi Luuk,
Unfortunately this is not what I want. I would like both y plot on one graph as lines with the space between them filled (as with my code above). I just want to adjust it so that regions where YData2 > YData1 the fill is red and when YData1 > YData2, the fill is the colour it is now. Attached is what I currently have but it shows the same colour during times when the lines criss-cross
Oops, excuse me. I'm not very familiar with plotting lines.
nevertheless, if you try something analogous to
if Ydata1 < Ydata2
fill stuff in fancy blue
fill stuff in red
I would expect that to work.
Thanks Luuk but I am not sure how to do that will the flipr function

Sign in to comment.