Find Local Extrema

Find local maxima and minima in the Live Editor

Description

The Find Local Extrema task lets you interactively find local maxima and local minima in data. The task automatically generates MATLAB^® code for your live script.

Using this task, you can:

• Find local maxima, minima, or both in data from a workspace variable.

• Adjust parameters to locate fewer or more extrema.

• Visualize the detected extrema.

For more information on Live Editor tasks, see Add Interactive Tasks to a Live Script.

Related Functions

Find Local Extrema generates code that uses the islocalmin and islocalmax functions.

Open the Task

To add the Find Local Extrema task to a live script in the MATLAB Editor:

• On the Live Editor tab, select Task > Find Local Extrema.

• In a code block in the script, type a relevant keyword, such as extrema, find, islocalmin, or max. Select Find Local Extrema from the suggested command completions. For some keywords, the task automatically updates one or more corresponding parameters.

Examples

Separated Minima

Interactively find local minima in a vector of data using the Find Local Extrema task in the Live Editor.

Create a vector of data relative to the timestamps in the vector t.

t = hours(linspace(0,3,15));
data = [2 4 6 4 3 7 5 6 5 10 4 -1 -3 -2 0];

Open the Find Local Extrema task in the Live Editor. Select data as the input data and t as the x-axis coordinates of the data.

Specify the extrema type as Minima in the Extrema type field. Then, specify the minimum separation between local minima as 0.5 hours and the prominence window as 1 hour using the Min separation field, the Prominence window field, and the units drop-down.

The title of the plot indicates that there are three local minima in data that are at least 0.5 hours apart.

You can use the output arguments of a Live Editor task in subsequent code. Use the indices returned by the task to determine the values of the local minima.

vals = data(minIndices)

vals = 1×3

     3     5    -3

Related Examples

• Add Interactive Tasks to a Live Script
• Clean Messy Data and Locate Extrema Using Live Editor Tasks

Parameters

Input data — Valid input data from workspace

vector | table | timetable

This task operates on input data contained in a vector, table, or timetable. The data can be of type single, double, logical, or signed or unsigned integer types such as int64.

When providing a table or timetable for the input data, select All supported variables to operate on all variables with a supported type. Select All numeric variables to operate on all variables of type single or double, or signed or unsigned integer types. To choose specific supported variables to operate on, select Specified variables and then select the variables individually.

Flat selection — Flat region indicator

Center (default) | First | Last | All

Specify a flat region indicator when you have local consecutive extrema values.

Method	Description
Center	Indicates only the center element of a flat region as the local extrema
First	Indicates only the first element of a flat region as the local extrema
Last	Indicates only the last element of a flat region as the local extrema
All	Indicates all the elements of a flat region as the local extrema

Min prominence — Minimum prominence of extrema

0 (default) | positive scalar

Specify a minimum prominence to return only local extrema whose prominence is at least that value. Higher prominence values return fewer detected extrema.

The prominence of a local maximum (or peak) is a measure of how the peak stands out with respect to its height and location relative to other peaks. The prominence of a local minimum (or valley) is a measure of how the valley stands out with respect to its depth and location relative to other valleys.

Prominence window — Window for computing prominence

Centered (default) | Asymmetric

Specify a prominence window type and size to define a window of neighboring points for which to compute the prominence for each local extrema.

Window	Description
Centered	Specified window length centered about the current point
Asymmetric	Specified window containing the number of elements before the current point and the number of elements after the current point

Window sizes are relative to the X-axis variable units.

Version History

Introduced in R2019b

R2022b: Plot multiple table variables

Simultaneously plot multiple table variables in the display of this Live Editor task. For table or timetable data, to visualize all selected table variables at once in a tiled chart layout, set the Variable to display field.

R2022b: Specify tabular output

Output a table or timetable with logical variables corresponding to the table variables checked for local extrema, or append the logical variables to the input table. For table or timetable input data, to specify the tabular format, set the Output format field.

R2022a: Live Editor task does not run automatically if inputs have more than 1 million elements

This Live Editor task does not run automatically if the inputs have more than 1 million elements. In previous releases, the task always ran automatically for inputs of any size. If the inputs have a large number of elements, then the code generated by this task can take a noticeable amount of time to run (more than a few seconds).

When a task does not run automatically, the Autorun indicator is disabled. You can either run the task manually when needed or choose to enable the task to run automatically.

R2021a: Operate on multiple table variables

This Live Editor task can operate on multiple table variables at the same time. For table or timetable input data, to operate on multiple variables, select All supported variables or Specified variables. Return all of the variables or only the modified variables, and specify which variable to visualize.