# Change plot color for increasing or decreasing x values

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Matt on 12 Aug 2014
Commented: Matt on 13 Aug 2014
Hi all...I'm pretty inexperienced with MATLAB so bear with me. I am trying to import a data set from a .txt file which has many cycles along the x-axis. Since the x-axis is temperature, I would like the increasing segment of each cycle curve (heating) to be red and the decreasing segment (cooling) to be blue. I'm not experienced enough to write a FOR loop to implement this, and I was unable to find a solution on the forums. Any help is much appreciated. Thanks!
Sara on 12 Aug 2014
Can you show a plot of your results?

Joseph Cheng on 12 Aug 2014
from what you described you don't really need a for loop to implement it. here is a solution to get away from a for loop
%my attempt to make something i think you're plotting.
%something like a Hysteresis curve.
y = [0 8 12 8 0 -8 -12 -8 0];
x = [2 10 10 8 -2 -10 -10 -8 2];
figure,plot(x,y)
%find which segments are heating and cooling or staying the same.
dx = diff(x); %takes x(n+1)-x(n)
heating = dx>0; %positive dx
steady = dx ==0; %0 dx (temp values didn't change)
cooling = dx<0; %negative dx.
plotSegmentX = [x(1:end-1);x(2:end)]; %pair the segments up.
plotSegmentY = [y(1:end-1);y(2:end)]; %pair the segments up.
%plot only the heating segments and color them red. then plot only the cooling etc.
figure,plot(plotSegmentX(:,heating),plotSegmentY(:,heating),'r',...
plotSegmentX(:,cooling),plotSegmentY(:,cooling),'b',...
xlim([-14 14]);ylim([-12 12])
Matt on 13 Aug 2014
that did the trick. everything looks great, except there is some noise in the data that causes small blue segments on the heating curve. is there a way to take the difference between two non-consecutive values? such as x(n+2)-x(n)? i think this would filter out the noise.