Marcos Duarte

Laboratory of Biomechanics and Motor Control](http://demotu.org/

Federal University of ABC, Brazil

One way to detect peaks (local maxima) or valleys (local minima) in data is to use the property that a peak (or valley) must be greater (or smaller) than its immediate neighbors. The function `detect_peaks.py`

from Python module `detecta`

detects peaks (or valleys) based on this feature and other characteristics. The function signature is:

```
ind = detect_peaks(x, mph=None, mpd=1, threshold=0, edge='rising', kpsh=False, valley=False, show=False, ax=None, title=True)
```

The parameters `mph`

, `mpd`

, and `threshold`

follow the convention of the Matlab function `findpeaks.m`

.

Let's see how to use `detect_peaks.py`

; first let's import the necessary Python libraries and configure the environment:

In [1]:

```
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline
from detecta import detect_peaks
```

Running the function examples:

In [3]:

```
>>> x = np.random.randn(100)
>>> x[60:81] = np.nan
>>> # detect all peaks and plot data
>>> ind = detect_peaks(x, show=True)
>>> print(ind)
>>> x = np.sin(2*np.pi*5*np.linspace(0, 1, 200)) + np.random.randn(200)/5
>>> # set minimum peak height = 0 and minimum peak distance = 20
>>> detect_peaks(x, mph=0, mpd=20, show=True)
>>> x = [0, 1, 0, 2, 0, 3, 0, 2, 0, 1, 0]
>>> # set minimum peak distance = 2
>>> detect_peaks(x, mpd=2, show=True)
>>> x = np.sin(2*np.pi*5*np.linspace(0, 1, 200)) + np.random.randn(200)/5
>>> # detection of valleys instead of peaks
>>> detect_peaks(x, mph=-1.2, mpd=20, valley=True, show=True)
>>> x = [0, 1, 1, 0, 1, 1, 0]
>>> # detect both edges
>>> detect_peaks(x, edge='both', show=True)
>>> x = [-2, 1, -2, 2, 1, 1, 3, 0]
>>> # set threshold = 2
>>> detect_peaks(x, threshold = 2, show=True)
>>> x = [-2, 1, -2, 2, 1, 1, 3, 0]
>>> fig, axs = plt.subplots(ncols=2, nrows=1, figsize=(10, 4))
>>> detect_peaks(x, show=True, ax=axs[0], threshold=0.5, title=False)
>>> detect_peaks(x, show=True, ax=axs[1], threshold=1.5, title=False)
```

Out[3]:

The function `detect_peaks.py`

is relatively fast but the parameter minimum peak distance (mpd) slows down the function if the data has several peaks (>1000). Try to decrease the number of peaks by tuning the other parameters or smooth the data before calling this function with several peaks in the data.

Here is a simple test of its performance:

In [4]:

```
x = np.random.randn(10000)
ind = detect_peaks(x)
print('Data with %d points and %d peaks\n' %(x.size, ind.size))
print('Performance (without the minimum peak distance parameter):')
print('detect_peaks(x)')
%timeit detect_peaks(x)
print('\nPerformance (using the minimum peak distance parameter):')
print('detect_peaks(x, mpd=10)')
%timeit detect_peaks(x, mpd=10)
```