How to find the peaks (both x and y location)

Question

For instance, if I was  plotting Scope (x) and Temperature (y), why can't I use the following code: [pks,locs] = findpeaks(Temperature)? Matlab tells me that there is the following error: Error using findpeaks>parse_inputs (line 131) Expected a string for the parameter name, instead the input type was 'double'.   Error in findpeaks (line 71) [X,Ph,Pd,Th,Np,Str,infIdx] = parse_inputs(Xin,varargin{:});   It gives me the peaks when I simply use findpeaks(Temperature), but I need the corresponding x values to compute as well.

John Michell · Accepted Answer

The error occurs because findpeaks expects additional inputs (parameters) to be specified as name-value pairs, and you might have accidentally passed a numeric input that caused confusion.
If you want both the peak values (y locations) and their corresponding x locations, you need to pass the x values explicitly as the first argument to findpeaks. Here's the correct way to do it:
Correct Code
 

[pks, locs] = findpeaks(Temperature, Scope);

Explanation

Temperature: Your y values (the data you want to find peaks for).
Scope: Your x values (the corresponding x-axis data for the peaks).

The output will be:

pks: The peak values in the Temperature array.
locs: The corresponding x values from the Scope array where the peaks occur.

Example
 
Scope = 1:0.1:10; % Example x-axis values
Temperature = sin(Scope) + 0.1*rand(size(Scope)); % Example y-axis values with noise

[pks, locs] = findpeaks(Temperature, Scope);

% Plot results
plot(Scope, Temperature);
hold on;
plot(locs, pks, 'ro'); % Mark peaks
xlabel('Scope');
ylabel('Temperature');
title('Peaks in Temperature Data');

Key Points

Ensure that Scope and Temperature have the same length.
Use findpeaks with both y and x inputs to get the correct x locations for the peaks.
If you need additional options (e.g., threshold, minimum peak distance), you can specify them as name-value pairs:

 
[pks, locs] = findpeaks(Temperature, Scope, 'MinPeakHeight', 0.5, 'MinPeakDistance', 10);

Let me know if you need further clarification!

How to find the peaks (both x and y location)

Correct Code

Explanation

Example

Key Points

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