Plot problem: How to mark a symbol "X".

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Phuc Tan Huynh
Phuc Tan Huynh 2016-5-6
编辑： Star Strider 2016-5-7
I had a question to plot two function on a graph, and for each intersection point of two function, mark a symbol "X". I don't know how to do it, Please help me.

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回答（1 个）

Star Strider
Star Strider 2016-5-6
If you have calculated the intersection as a (xi,yi) pair, use the hold command, and then:
plot(xi, yi, 'x')
  2 个评论
Phuc Tan Huynh
Phuc Tan Huynh 2016-5-6
Oh well, thanks for your help but it is still confused for me. I already use fzero to find these intersection points of these two function and displayed these out. So how can I declare xi and yi like you said ???
Star Strider
Star Strider 2016-5-6
编辑：Star Strider 2016-5-7
My pleasure.
I would have to see your code.
However, if you used fzero, you probably have the ‘xi’ coordinates, and since fzero requires a function that most likely subtracts one function from another, you would use that value in one of the functions you used to calculate ‘xi’ to calulate ‘yi’.
Example:
f1 = @(x) 10 - 5*x;
f2 = @(x) x.^2 + 1;
xi = fzero(@(x) f1(x)-f2(x), 1);
t = linspace(0, 3);
figure(1)
plot(t, f1(t), '-b', t, f2(t), '-g')
hold on
plot(xi, f1(xi), 'xr', 'MarkerSize',20)
hold off
grid

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