How would I plot this and then achieve minimum and maximum.
3 次查看(过去 30 天)
显示 更早的评论
This is the equation
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1545757/image.png)
My script looks like this and fails
x=0:0.1:15
y=(x)^3/3-11(x)^2/2+24x
plot(x,y)
Not yet got my head around MatlB
采纳的回答
Les Beckham
2023-11-21
编辑:Les Beckham
2023-11-21
x = 0:0.1:15;
% y=(x)^3/3-11(x)^2/2+24x << you were missing multiplication operators *
% and the powers need to be .^ (element-wise operator) instead of ^ (matrix
% operator)
y = x.^3 / 3 - 11*x.^2 / 2 + 24*x;
plot(x, y)
grid on
xlabel x
ylabel y
fprintf('min(y) = %f; max(y) = %f\n', min(y), max(y))
Also, if you are just getting started with Matlab, I would highly recommend that you take a couple of hours to go through the free online tutorial: Matlab Onramp
更多回答(1 个)
Sam Chak
2023-11-21
Hi @Tom
The cubic function does not have global extrema, but it does have a local maximum point and a local minimum point. Are you looking to plot something similar to this?
%% Find local max and local min over a certain range
y = @(x) x.^3/3 - 11*x.^2/2 + 24*x;
xlocal = linspace(1, 10, 90001);
ymax = max(y(xlocal))
idx1 = find(y(xlocal) == ymax);
xmax = xlocal(idx1)
ymin = min(y(xlocal))
idx2 = find(y(xlocal) == ymin);
xmin = xlocal(idx2)
%% Plot function over a predefined range
x = 0:0.1:15;
plot(x, y(x)), grid on, hold on
plot(xmax, ymax, 'o', 'markersize', 12, 'linewidth', 2)
plot(xmin, ymin, 'o', 'markersize', 12, 'linewidth', 2)
xlabel('x'), ylabel('y')
xt = [xmax-1 xmin-1];
yt = [ymax+15 ymin+15];
str = {'local max','local min'};
text(xt, yt, str)
2 个评论
Dyuman Joshi
2023-11-21
I'm a curious as to why you chose to use max() and min() instead of islocalmax() and islocalmin().
Sam Chak
2023-11-22
Sometimes, I'm accustomed to using functions with the same name in other software. It's good that you introduced islocalmax() and islocalmin().
另请参阅
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!