creating a rainbow colour plot/trajectory

I was reading this:

https://uk.mathworks.com/matlabcentral/answers/393810-multiple-colours-in-a-trajectory-plot

to create a rainbow coloured plot. I have data points X(:,1) and X(:,2) (Both x and y axis). I do not understand how to use the function in the link to create a trajectory with rainbow colours.

Please help.

Answer 1

[KSSV]

clc; clear all ;
x = 1:50 ; 
y = rand(size(x)) ;
z = zeros(size(x)) ;
col = x;  % This is the color, vary with x in this case.

surface([x;x],[y;y],[z;z],[col;col],...
        'facecol','no',...
        'edgecol','interp',...
        'linew',2);

[cgo]

thank you for your response. the expectation i have is one ROYGBV spectrum (red start and violet end).

But the real plot I have is more than one spectrum. why is this?

[KSSV]

The code used a deafult colormap......you need to set your colormap....read about cmap

Answer 2

[Mehmed Saad]

You can use surface or patch for that purpose but not plot

I am going to describe how to do it with patch

figure,plot(1:3,[1 -1 1],'r')

Now replace plot with patch (remember patch needs polygon Color)

figure,patch(1:3,[1 -1 1],'r')

So patch creates a patch between [1 -1 1] and join the the first and last point at the end (to complete the patch)

red is the facecolor (PolyGon Color) of patch we passed in the 3rd argument of the function. and black is by defailt EdgeColor of patch object.

To change EdgeColor we can

figure,plot(1:3,[1 -1 1],'r','EdgeColor','c')

Now if we just want to draw the line and not the area patch is covering

figure,patch(1:3,[1 -1 1],'r','FaceColor','None')

but it will still join the first and last element. In order to stop that, insert another element at the end and set its value to NaN

figure,patch(1:4,[1 -1 1 NaN],'r','FaceColor','None')

Now Patch EdgeColor has following options

1. when you pass RGB value all edges will be of same color
2. when you pass 'flat' argument to EdgeColor, it will change Color after every Edge
3. when you pass 'interp' it will linearly interpolate betweeen two edges

For RGB

figure,patch(1:4,[1 -1 1 NaN],'r','EdgeColor','g')

For Flat, only two Colors 1:2 , 2:3 (there's also third color which is not visible because line is leading to NaN)

figure,patch(1:4,[1 -1 1 NaN],4:-1:1,'EdgeColor','flat')

figure,patch(1:4,[1 -1 1 NaN],4:-1:1,'EdgeColor','interp')
colormap('jet')

when you select interp for EdgeColor or FaceColor, then 3rd Argument (Polygon Color) should be change