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Gradient plot as arrow - strange result

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Gennaro Arguzzi
Gennaro Arguzzi 2017-11-12
评论： Jan 2017-11-12
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.

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Jan
Jan 2017-11-12
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)
  2 个评论
Gennaro Arguzzi
Gennaro Arguzzi 2017-11-12
编辑：Gennaro Arguzzi 2017-11-12
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
Jan 2017-11-12
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

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