What does u and v represent in a quiver plot?

I am confused regarding what u and v represent in a quiver plot. Let's make a real simple example.

x =[1];

y =[1];

My data point ends up moving from 1,1 to 3,3.

x2 =[3];

y2 =[3];

I use 3,3 for the u and v and it seems to plot an arrow that is pointing in the right direction.

My issue is I don't understand what u and v actually are. Is that starting and ending location like my example above? I have searched and find a lot of "u" and "v" used as notation but the "help quiver" does not seem (unless I messed it) to explain exactly what u and v are.

Answer 1

[Star Strider]

The (u,v) arguments are the derivatives of the plotted curve in the (x,y) directions, respectively. The easiest way to calculate them is to use the gradient function on each (x,y) vector, if you do not already have them from your data.

[Eric Snyder]

Perfect. That was really helpful.

[Star Strider]

Thank you.

My pleasure.

Answer 2

[dpb]

"A quiver plot displays velocity vectors as arrows with components (u,v) at the points (x,y)."

The (u,v) are the x- and y- components of the variable (often velocity; can be any directed quantity, of course, depending on the problem space) at the location in (x,y).

See the first example that should make that clear...

[Eric Snyder]

Yeah... I saw the first example before I posted. It was still not clear. The first example makes the mechanics clear but to me... not the concepts.

[dpb]

Oh. Well, my bad, then. I thought the cos(),sin() made it pretty clear. commonly it is the gradient of the field itself but one might want to associate another variable at the point so it isn't necessarily so.