Gradient coloring of streamlines

Hello,

I'm currently using the streamline function https://fr.mathworks.com/help/matlab/ref/streamline.html to plot the streamlines of a flow I'm considering. I would like to have an "evoluting" color along the streamlines according to the flow speed in each point.

I don't know how to start ... Any hint will be very appreciated ! Here is my code that is ploting the streamlines :

%%%%%%%%%%%%%%%%%Shear over topo

alpha = 70 ;
lambda = 20 ;

k = cosd(alpha) * 2 *pi/lambda ;
l = sind(alpha) * 2 *pi/lambda ;

x = 0 : 0.1 : 50 ;
y = 0 : 0.1 :50 ;

A = 1;
B = 3 ;
Amp = 0.1/sqrt(k^2+l^2) ;

[X,Y] = meshgrid(x,y) ;

TauX = Amp * sqrt(A^2+B^2)*(k^2/sqrt(k^2+l^2)).*cos(k.*X+l.*Y + atan(B/A)) ;
TauY = Amp * sqrt(A^2+B^2)*(k*l/sqrt(k^2+l^2)).*cos(k.*X+l.*Y + atan(B/A)) ;

Topo = Amp .* cos(k.*X + l.*Y) ;

figure
imagesc(x,y,Topo)
hold on
hlines = streamline(X(1:step:end,1:step:end),Y(1:step:end,1:step:end),1 + TauX(1:step:end,1:step:end), TauY(1:step:end,1:step:end),0*y(1:step:end,1:step:end),y(1:step:end,1:step:end)) ;
set(hlines, 'Color', 'k')

Thank you very much !

Answer 1

[Manish Annappa]

As per your description, you either want to set different colors to each line in variable 'hlines' or you want to set multiple colors to a single line (varying colors along Y axis).

1) You can set different colors to each line using the code snippet below.

colorstring = 'kbgry';
for i = 1:5
  set(hlines(i), 'Color', colorstring(i))
end

2) As per the link below, it is not possible to set different colors for different region of a line.

https://www.mathworks.com/matlabcentral/answers/283946-how-to-plot-one-line-with-multiple-colors

However, below link that illustrates the usage of patch objects may help you.

https://www.mathworks.com/matlabcentral/answers/21382-plot-different-color