Hướng dẫn dùng python loglog python

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Prerequisites: Matplotlib

Matplotlib is a comprehensive library for creating interactive, static and animated visualizations in python. Using general-purpose GUI toolkits like wxPython, SciPy, Tkinter or SciPy, it provides an object-oriented API for embedding plots into applications. Matplotlib.pyplot is a collection of functions that makes Matplotlib work like MATLAB.

Here, we will be exploring loglog() function of Matplotlib.pyplot. It is used to plot a log scale over both x and y-axis.

Syntax:

loglog(X,Y)

Where,

X and Y refer to x and y coordinates respectively.

Other function used is linespace(). It returns evenly spaced numbers over a specified interval.

Syntax:

np.linspace(start, stop, num, endpoint, retstep, dtype, axis)

Where,

• Start : The starting value of sequence from where you want to show the line, or we can say starting point of line
• Stop : It is the end value of the sequence at where the line stops, unless ‘endpoint’ is set to False.
• Num : Number of samples to generate. Must be non-negative. By default, it is 50.
• Endpoint : It works same as stop. If it is True then stop is the last sample else stop is excluded from the sequence.
• Retstep : If True, return (‘samples’, ‘step’), where `step` is the spacing between samples.
• Dtype : The type of the output array.
• Axis : The axis in the result to store the samples and it is relevant only if start or stop are array-like

Example : Without loglog()

Python

import matplotlib.pyplot as plt

import numpy as np

x_input = np.linspace(0, 10, 50000)

y_input = x_input**8

plt.plot(x_input, y_input)

Output: 

Example : With loglog()

Python3

import matplotlib.pyplot as plt

import numpy as np

x_input = np.linspace(0, 10, 50000)

y_input = x_input**8

plt.loglog(x_input, y_input)

Output:

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Matplotlib is a library in Python and it is numerical – mathematical extension for NumPy library. The Axes Class contains most of the figure elements: Axis, Tick, Line2D, Text, Polygon, etc., and sets the coordinate system. And the instances of Axes supports callbacks through a callbacks attribute.

matplotlib.axes.Axes.loglog() Function

The Axes.errorbar() function in axes module of matplotlib library is used to make a plot with log scaling on both the x and y axis.

Syntax:

Axes.loglog(self, *args, **kwargs)

Parameters: This method accept the following parameters that are described below:

• basex, basey: These parameter are Base of the x/y logarithm and are optional with default value 10.
• subsx, subsy: These parameter are the sequence of location of the minor x/y ticks and are optional.
• nonposx, nonposy: These parameter are non-positive values in x or y that can be masked as invalid, or clipped to a very small positive number.

Returns: This returns the following:

• lines:This returns the list of Line2D objects representing the plotted data..

Below examples illustrate the matplotlib.axes.Axes.loglog() function in matplotlib.axes:

Example-1:

import numpy as np

import matplotlib.pyplot as plt

t = np.arange(0.01, 20.0, 0.01)

fig, ax = plt.subplots()

ax.loglog(t, 20 * np.exp(-t / 10.0), basex = 2)

ax.set_title('matplotlib.axes.Axes.loglog Example2')

plt.show()

Output:

Example-2:

import numpy as np

import matplotlib.pyplot as plt

fig, ax = plt.subplots(constrained_layout = True)

x = np.arange(0.02, 1, 0.02)

np.random.seed(19680801)

y = np.random.randn(len(x)) ** 2

ax.loglog(x, y)

ax.set_xlabel('f [Hz]')

ax.set_ylabel('PSD')

ax.set_title('Random spectrum')

def forward(x):

    return 1 / x

def inverse(x):

    return 1 / x

ax.set_title('matplotlib.axes.Axes.loglog Example2')

plt.show()

Output: