findextremum

[xmin, ymin, xmax, ymax] = findextremum(x, y, winlen, dispout)

Description

Find local extremum (minimum and maximum) in data

Inputs

x

x data

y

y data

winlen=3;

Window length, defines a number of points in sliding window used for defining maximum and minimum

Example: winlen=5 means two points on each side of each data point is used in calculation

Using a larger value for winlen makes it less sensitive

winlen should be an odd number equal or larger than 3

dispout=’no’;

Define to display outputs or not (‘yes’: display, ‘no’: not display)

Outputs

xmin

x of minmum points

ymin

y of minmum points

xmax

x of maximum points

ymax

y of maximum points

Examples

x(:,1)=linspace(0,30,1000);
y=2.*exp(-0.1*2*pi/5.*x).*sin(sqrt(1-0.1^2)*2*pi/5.*x);
[xmin,ymin,xmax,ymax]=findextremum(x,y,3,'yes');

x(:,1)=linspace(0,50,1000);
y(:,1)=sin(x)+0.1.*rand(1000,1);
[xmin,ymin,xmax,ymax]=findextremum(x,y,15,'yes');

References