Gradient plot as arrow - strange result

I tried to plot gradient as an arrow with:

    x=-10:2:10;
    f = -x.^2;
    u = gradient(x);
    n=length(u);
    for i=1:n
        a(i)=0;
    end
    quiver(a,a,u,a)
    grid
    axis equal

Why I get only one arrow? I'd like to get an arrow each two x ticks.

Thank you very much in advance.

Answer 1

[Jan]

You do not get only 1 arrow, but they all start from the same point and have the same size and direction. Try:

quiver(x, f, u, a)

[Gennaro Arguzzi]

Hello @JanSimon, how can I get the following result? Arrows are right scaled and not superimposed. This is the gradient in one dimension.

Thank you so much.

[Jan]

x  = -10:2:10;
f  = -x.^2;
df = gradient(f, x);
figure;
plot(x, f);
hold on
quiver(x, zeros(size(x)), df/10, zeros(size(x)), 0, 'r');

Well, this is extremely ugly. I was not able to use quiver at any time for any useful output. There are many nice arrow functions in the FileExchange: https://www.mathworks.com/matlabcentral/fileexchange/?utf8=%E2%9C%93&term=arrow