How do I change the direction of a quiver vector at the same time change the sign of its magnitude ?

Hi! I am plotting a velocity field with the help of quiver. I want to reverse the direction of some of the vectors, but at the same time, want to change the sign of its magnitude. For example, if the vector is pointing in negative Y direction with a magnitude of 10 units, I want it to point in positive Y direction with the magnitude of -10 units so that the meaning of the vector remains the same. How do I do this in MATLAB ?

Answer 1

[KSSV]

You can change the direction of y by using quiver(x,y,u,-v) instead of quiver(x,y,u,v).

Coming about magnitude, it is given by sqrt(u^2+v^2). You have no control on it's sign. It will be always positive.

Answer 2

[SOURAV KUMAR]

Hi @Kushal Joshi ,

You can use quiver(x0,y0,-v1,-v2) instead of quiver(x0,y0,v1,v2) to reverse a vector

For Example, consider the following code:

    clc
    clear all
    close all
    x0=1;
    y0=2;
    v1=-1;
    v2=1;
    quiver(x0,y0,v1,v2,'r')
    hold on
    quiver(x0,y0,-v1,-v2,'g')
    legend('Original Vector','Reverse Vector')
    hold on
    plot(x0,y0,'k*')

Output:

Note: It will be incorrect to use the term magnitude as magnitude of a vector is always positive;

However you can say to change the sign of the vector,

i.e., If original vector is , then desired vector is