How to change the color of only some arrows using quiver?

Hi everyone,

I would like to know if it is possible to change the color of only some of the arrows using quiver.

I tried to selected the data that I want with different color and plot a second quiver plot. Something like that:

figure
q1 = quiver(x,y,u,v)
hold on
q2 = quive(x(color2),y(color2),u(color2),v(color2))

The problem is that the size of the arrow of both plots doesnt match, although u and v are the same. Here is an example. We can see that the blue arrows are bigger than the magenta ones.

I suppose that is a problem in the function, related to the scale of the arrows. When the data for both quivers are the same, the problem does not happen.

I have tried to zero or NaN the data of the second quiver, instead of select with a filter, but it didnt solve the problem.

I am wonder if anyone have already the same problem and could help me.

Thank you!

Answer 1

[Bjorn Gustavsson]

From the help of quiver:

    quiver(U,V,S) or quiver(X,Y,U,V,S) automatically scales the
    arrows to fit within the grid and then stretches them by S.  Use
    S=0 to plot the arrows without the automatic scaling.

So if you try to set S to something specified you might avoid the different scalings of your arrows. You might also try the different arrow-functions on the file-exchange which might give you more detailed controll over the arrows. See for example: arrow and arrow3 (they have a different set of the input arguments but that is manageable).

HTH

[Marcos Ortensi]

You are right!

I thought that seting S=0 would make all the vector's size equals to 1, but it only use the same unit of the axis.

Now I can set S=0 and add a scale manually multiplying my u and v.

Thank you very much!

[Bjorn Gustavsson]

Glad that it helped.