Marking x intercepts on graph
显示 更早的评论
Sorry everyone. I'm pretty new to matlab. My question was to graph an equation V against x for -4</= x </=4
This is the code I came up with:
x=linspace(-4,4);
V=(x.^3/3)-4*x;
plot(x,V)
xlabel('Position'),ylabel('Potential Energy')
I need to mark the x-intercepts on the graph. How do I go about doing that?
采纳的回答
Method 1: solve equation for y=0
Use the Symbolic Math Toolbox to solve for y=0; see inline comments for details.
% Solve for y=0
syms x
eqn = x.^3/3-4*x == 0;
xInt = double(solve(eqn)); % X values where y=0
yInt = zeros(size(xInt)); % Corresponding y values (all 0)
% plot function and x-intercepts
x=linspace(-4,4);
V=(x.^3/3)-4*x;
plot(x,V,'k-')
hold on
plot(xInt,yInt, 'm*','MarkerSize', 10)
yline(0)
Method 2: use intersections() to find x-intercepts
This uses the intersections() function from the file exchange to find the (x,y) coordinates of the x-intercepts.
x=linspace(-4,4);
V=(x.^3/3)-4*x;
[xInt,yInt] = intersections(x,V,x,zeros(size(V)));
% ^^ ^^ There are your intercept coordinates
plot(x,V,'k-')
hold on
plot(xInt,yInt, 'm*','MarkerSize', 10)
yline(0)
Both methods produce this figure
8 个评论
Daniel Matthew
2019-11-15
Adam Danz
2019-11-16
@Daniel Matthew, I just added "Method 1" to my answer. It uses the Symbolic Math Toolbox to solve your equation for y=0 and therefore does not depend on a 3rd party FEX function.
Abdennaser Hadab
2022-10-15
The second method pops an error:
Undefined function 'intersections' for input arguments of type 'double'.
Any idea what is wrong?
Adam Danz
2022-10-17
@Abdennaser Hadab, the sentence under the "Method 2" heading tells you the answer and has a link :)
Abdennaser Hadab
2022-10-18
编辑：Abdennaser Hadab
2022-10-18
@Adam Danz thanks, I have been a bit confused but I realized I needed to download the file and put it in the same folder where my .m file is in order to call for the function with no issues.
I did not know I had to do this.
Adam Danz
2022-10-18
@Abdennaser Hadab, you figured it out! You can either add the file to the same folder containing the main m-file or you can store the file anywhere and make sure you add the path to the file using addpath in the m-file.
Abdennaser Hadab
2022-10-19
@Adam Danz thank for the tip!
Shyamini
2024-1-24
@Adam Danz Thank you so much!! this helped tremendously
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