how to determine each local min point?

1 次查看(过去 30 天)
Hi everyone, I have a urgent question to seek for help...
I have a sine wave however, angle in the sine wave is not a constant variation of x as shown below...
x = 0: 0.00001: 4;
v = x.*exp(x/2);
t = sin(v);
plot(x,t);
My trouble is how to display each of the local xmin point?
From the plot itself i wanted to display xmin1 = 1.859, xmin2 = 2.73, and xmin3 = 3.307.
Hope to hear from anyone soon... been cracking my head for the past weeks... )':
Best Regards
Will*

采纳的回答

Image Analyst
Image Analyst 2013-3-6
编辑:Image Analyst 2013-3-6
If you have the Image Processing Toolbox, you can use imregionalmin(), like this:
% Original code
x = 0: 0.00001: 4;
v = x.*exp(x/2);
t = sin(v);
plot(x,t);
% Image Analyst's code:
minsIndexes = imregionalmin(t); % Logical array of where mins are.
% Extract the t values at those min locations;
minValues = t(minsIndexes)
% Get the x values at those mins.
minX = x(minsIndexes)
% Plot star over the mins.
hold on;
plot(minX, minValues, 'r*', 'MarkerSize', 10);
In the command window:
minValues =
0 -1.00 -1.00 -1.00 -1.00 -0.96
minX =
0 1.86 2.76 3.31 3.70 4.00

更多回答(1 个)

Matt J
Matt J 2013-3-6
编辑:Matt J 2013-3-6
k=3; %Do this for all desired k>=0
xmin=fzero(@(x) x.*exp(x/2) - 2*pi*k,0)
  1 个评论
Matt J
Matt J 2013-3-6
There is also a minimum at x=-2, as elementary calculus can tell you.

请先登录,再进行评论。

类别

Help CenterFile Exchange 中查找有关 MATLAB 的更多信息

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by