×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# local extrema

## local extrema

(OP)
Hello everybody!

I am trying to determine and plot the local extrema (min(max) and max(min)) for the signal y=x.*w with x(400:1424)=sin(2*pi*t) and w(400:1424)=sin(52*pi*t).

I am using matlab 2010b with the following script:

clc
clear all

Fs=1024;
t = 0:1/Fs:1;
x=zeros(1,1824);
w=zeros(1,1824);
vm=1;vc=2

x(400:1424)=sin(2*pi*t);
w(400:1424)=sin(52*pi*t);
y=x.*w;

figure(1);
plot(y); hold on;

Is there anyone with an idea how to accomplish this?

### RE: local extrema

(OP)
The min(max) is the minimum of the local maximum when you use a slide window on a signal. Max(min) is the opposite: the maximum of the local minimum.

It creates the upper envelope and lower envelope of the signal.

### RE: local extrema

I was a bit confused by your use of indexing, but maybe this will get you started?

#### CODE --> MATLAB

f   = inline(vectorize('sin(w1*t)*sin(w2*t)'),'t','w1','w2');
df  = inline(vectorize('w1*cos(w1*t)*sin(w2*t)+w2*sin(w1*t)*cos(w2*t)'),...
't','w1','w2');
ww1 = 2*pi;
ww2 = 52*pi;
tmin= 0; tmax= 1;
inc  = 0.01; k=1;
t = [tmin, tmin+inc];   %Set initial search range
while t(1) <= tmax
% Check for sign change within search range
A = sign(df(t(1),ww1,ww2));
B = sign(df(t(2),ww1,ww2));
if A~=B % If sign change, find where derivative equals zero
tt(k) = fzero(@(t) df(t,ww1,ww2), t);
k     = k+1;
t     = [t(2), t(2)+inc];
else
t(2)=t(2)+inc;  % If no sign change, increase search field
end
end 

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!