how to get a plot quiver with velocity magnitude

How to get a quiver plot with change in color basing on velocity vector magnitude

Answer 1

[Priyanshu Mishra]

Hi Bharathi,

You can use 'color' linespec to change the color of your velocity vectors. For your reference I have written a code. You may take help of it.

[x,y] = meshgrid(0:0.2:2,0:0.2:2);

u = cos(x).*y;

v = sin(x).*y;

figure

quiver(x,y,u,v,'color',[1 0 0])

The above code will give you red color velocity vectors. By changing the linespec for eg. [1 1 0], it will give you yellow color.

[Daniele Morandi]

Hi Priyanshu,

I guess that Bharathi meant that color could change depending on velocity magnitude, similarly to what happen in contour plot.

Colorbar should help reading magnitude related to color, if this is possible

Answer 2

[Gautam]

Hello bharathi

The “quiver” function in MATLAB does not natively support color coding based on vector magnitude. However, you can achieve this by plotting each vector individually and setting the color according to its magnitude

[x,y] = meshgrid(-pi:pi/8:pi,-pi:pi/8:pi); 
vx = sin(y); 
vy = cos(x); 
magnitude = sqrt(vx.^2 + vy.^2); 
magnitude_normalized = (magnitude - min(magnitude)) ./ (max(magnitude) - min(magnitude)); 
cmap = jet(256); 
figure; 
hold on; 
for i = 1:length(x) 
    for j=1:length(y) 
        % Determine color index 
        color_idx = round(magnitude_normalized(i,j) * (length(cmap) - 1)) + 1; 
        % Plot vector with color 
        quiver(x(i,j), y(i,j), vx(i,j), vy(i,j),1, 'Color', cmap(color_idx, :)); 
    end 
end 
hold off; 
colorbar;
colormap(cmap);

This produces the following output