MATLAB Answers

plot graphic with different color

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Giuseppe Dibenedetto
Giuseppe Dibenedetto on 14 Feb 2020
Commented: fred ssemwogerere on 14 Feb 2020
Hi,
I have a data set made by two vector x and y.
I need to plot it to obtain an effect like the one attached.
So i need the lines to be green if y >= 0,
and red elsewhere.
Can anyone help me?

  1 Comment

Bob Nbob
Bob Nbob on 14 Feb 2020
If you have a pair of vectors, x and y, how are you getting lines? Are you using the x and y values of corresponding elements in the vectors to make cartesian coordinates? Are you connnecting these coordinates to each other or to a common point?
Do you have any code that you have written out so far?

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Answers (2)

fred  ssemwogerere
fred ssemwogerere on 14 Feb 2020
Hello, with logical indexing, you could create two separate pairwise sets of data, with one set comprised of plots of x versus y-data greater than zero, and another set comprised of x and y-values less than zero. These can then be plotted on the same figure but with different 'color' properties.

  1 Comment

fred  ssemwogerere
fred ssemwogerere on 14 Feb 2020
Something like:
% Assuming your 'x' and 'y' vectors as;
x=[3 2 4 3 5 1];y=[-1 3 -5 2 -3 6];
% For y>0, use logical indexing to create separate set, while also choosing the corresponding values in 'x'
x1=x(y>0);y1=y(y>0);
% Do the same for y<0
x2=x(y<0);y2=y(y<0);
% Go ahead and plot (assuming you are using the 'plot' function)
figure
handl1=plot(x1,y1,'-r');
hold on
handl2=plot(x2,y2,'-g');
hold off

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Bob Nbob
Bob Nbob on 14 Feb 2020
If you're using the plot command, it is relatively easy to define a different color for a plot. Setting the condition where this color applies is more difficult, and requires we have a better understanding of your application to answer.
plot(x,y,'g'); % Plot the x and y values as cartesian coordinates with a green line connecting them.

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