Advanced Plotting and Model Building - FET

Visualizing vector fields
The function quiver draws little arrows to indicate a gradient
or other vector field. Although it produces a 2-D plot, it’s
often used in conjunction with contour. As an example,
consider the scalar function of two variables
V = x 2 + y. The gradient of V is defined as the vector field
∇V = ( ∂V / ∂x , ∂V / ∂y ) = (2x, 1).
The following statements draw arrows indicating the
direction of ∇V at points in the x-y plane (see the next figure).
[x y] = meshgrid(-2:.2:2, -2:.2:2);
V = x.^2 + y;
dx = 2*x;
dy = dx; % dy same size as dx
dy(:,:) = 1; % now dy is same size as dx but all 1’s
contour(x, y, V), hold on
quiver(x, y, dx, dy), hold off
5-68
Z.R.K