[x,y] = meshgrid(-2:0.25:2, -2:0.25:2);
slope = x - y;
% Vectors with components (1, slope) have the desired slope.
z = ones( size(slope) );
% Normalize to make all mini-tangents have the same length.
sx = z./(10*sqrt( z.^2 + slope.^2 ));
sy = slope./(10*sqrt( z.^2 + slope.^2 ));
% Plot mini-tangents...
quiver(x,y,sx,sy,0,'ShowArrowHead','off')
hold on
% ... on both sides of grid points.
quiver(x,y,-sx,-sy,0,'ShowArrowHead','off')

% Add some solutions.
x=-2:.01:2;
for c=-1:3
  y=x-1+c*exp(-x);
  plot(x,y,'linewidth',5)
end
axis([-2 2 -2 2]);
title("Slope field for y'=x-y with five soln's");