Changing color of plot

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Thomas Wans
Thomas Wans on 24 Oct 2021
Commented: Rik on 27 Oct 2021
Hi,
I need to make plot that has two colors of line red and blue, and the line should be red when value is increasing and blue when value is decreasing and when I use dotted line it works 'b*' but without this it doesn't work 'b' I think I should define first point of plot but I'm not sure.
x = -10:.01:10;
for ii = 1:length(x)
y(ii) = sin(x(ii)); % Data point ii has come in.
if y(ii)<0
c = 'b*';
else
c = 'r*';
end
plot(x(ii),y(ii),c)
hold on
end
  2 Comments
Rik
Rik on 27 Oct 2021
You don't get it, do you? I'm probably more stubborn than you. I will keep restoring your edit, so you might as well give up now.
Changing color of plot when value is increasing
Hi,
I need to make plot that has two colors of line red and blue, and the line should be red when value is increasing and blue when value is decreasing and when I use dotted line it works 'b*' but without this it doesn't work 'b' I think I should define first point of plot but I'm not sure.
x = -10:.01:10;
for ii = 1:length(x)
y(ii) = sin(x(ii)); % Data point ii has come in.
if y(ii)<0
c = 'b*';
else
c = 'r*';
end
plot(x(ii),y(ii),c)
hold on
end

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Answers (1)

Sargondjani
Sargondjani on 24 Oct 2021
The problem is that you plot only 1 point at a time. So there is no line to plot, just a point. That's why your code doesn't work when you only specify a line type, for example c = '-b';
You could plot line segments:
plot([x(ii-1),x(ii)],[y(ii-1),y(ii)],c)
Another thing: you mention that you want it to be red, when value is increasing, so you criterion should be y(ii)>y(ii-1).
So your code becomes:
x = -10:.01:10;
y = sin(x);
for ii = 2:length(x)
if y(ii)>y(ii-1)
c = '-b';
else
c = '-r';
end
plot([x(ii-1),x(ii)],[y(ii-1),y(ii)],c)
hold on
end

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