QUIVER(X,Y,DX,DY) draws little arrows at every (X,Y) pair in
matrices X and Y. The (DX,DY) pairs in matrices DX and DY
determine the direction and magnitude of the arrows.
QUIVER(x,y,DX,DY), with two vector arguments replacing the first
two matrix arguments, must have length(x) = n and
length(y) = m where [m,n] = size(DX) = size(DY). In this case, the
arrows are the quads (x(j), y(i), DX(i,j), DY(i,j)).
Note that x corresponds to the columns of DX and DY and y corresponds
to the rows.
QUIVER(DX,DY) uses x = 1:n and y = 1:m. In this case DX and DY
are defined over a geometrically rectangular grid.
QUIVER(X,Y,DX,DY,S) and QUIVER(DX,DY,S) apply scalar S as a scale
factor to the lengths of the arrow. For example, S = 2 doubles
their relative length and S = 0.5 halves them.
A final trailing string argument specifies linetype and color using
any legal line specification as described under the plot command.
For example, try
xord = -2:.2:2;
yord = -2:.2:2;
[x,y] = meshgrid(xord,yord);
z = x .* exp(-x.^2 - y.^2);
[px,py] = gradient(z,.2,.2);
contour(x,y,z),hold on, quiver(x,y,px,py), hold off
See also GRADIENT , COMPASS , FEATHER , ROSE .