Graph of a 2D vector field equation and its divergence

Visualize vector field using quiver and divergence using filled contour at given 2D coordinates

%% Divergence of Vector Function with 2 Independent Variables
% by Prof. Roche C. de Guzman

%% Given
f = @(x,y) [(-4*x).*exp(-(x.^2)-y.^2); (-4*y).*exp(-(x.^2)-y.^2)]; % anonymous fx: f(x,y)
xi = -2; xf = 1; yi = -2; yf = 1; n = 10; % independent variables: initial and final values, and number of elements