Fill plot with gradient colors

I'm trying to plot a signal, for example cos(x), with a red gradient colormap for positive values and a blue one for negative values. Something similar to the solution previously discussed in:

https://www.mathworks.com/matlabcentral/answers/847360-filling-inside-of-a-plot-with-color-gradient

I haven't been able to make this work for me, any suggestions?

[Star Strider]

I posted this Comment responding to a similar Comment in the referenced post.

[Sergio Yanez-Pagans]

Thanks Strider!

Answer 1

[Dave B]

Here's one way to make the patch with the color gradient:

x=linspace(0,4*pi,100);
y=cos(x);
patch([x flip(x)],[y zeros(size(y))],[y zeros(size(y))])

You could use jet or turbo to have blue on the bottom and red on the top:

figure
patch([x flip(x)],[y zeros(size(y))],[y zeros(size(y))])
colormap jet

Or you could mix hot and cool colormaps:

figure
patch([x flip(x)],[y zeros(size(y))],[y zeros(size(y))])
colormap([cool;hot])

Or you could make your own colormap, just plug in red green and blue values that suit you (first column is red, second column is green, third column is blue):

figure
patch([x flip(x)],[y zeros(size(y))],[y zeros(size(y))])

cmap = ones(256,3);
cmap(129:256,2)=linspace(0,1,128);
cmap(129:256,3)=linspace(0,1,128);
cmap(1:128,1)=linspace(1,0,128);
cmap(1:128,2)=linspace(1,0,128);
colormap(cmap);

Answer 2

[Sergio Yanez-Pagans]

Thank you Dave, that was really useful!

Excellent answer =)