How do you fit a graph in python?

Have a look at

https://docs.scipy.org/doc/scipy-0.19.0/reference/generated/scipy.optimize.curve_fit.html,

there is an example at the bottom, which pretty much does what you are after.

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import matplotlib.pyplot as plt;
import numpy as np;
import scipy.optimize as opt;

# This is the function we are trying to fit to the data.
def func(x, a, b, c):
     return a * np.exp(-b * x) + c

# Generate some data, you don't have to do this, as you already have your data
xdata = np.linspace(0, 4, 50)
y = func(xdata, 2.5, 1.3, 0.5)
y_noise = 0.2 * np.random.normal(size=xdata.size)
ydata = y + y_noise

# Plot the actual data
plt.plot(xdata, ydata, ".", label="Data");

# The actual curve fitting happens here
optimizedParameters, pcov = opt.curve_fit(func, xdata, ydata);

# Use the optimized parameters to plot the best fit
plt.plot(xdata, func(xdata, *optimizedParameters), label="fit");

# Show the graph
plt.legend();
plt.show();

The x, y data are the xdata and ydata variables.

So if you want to use this code, just take out the bit where the data is generated, and define your x, y data arrays as "xdata" and "ydata".

Demos a simple curve fitting

First generate some data

import numpy as np

# Seed the random number generator for reproducibility
np.random.seed(0)

x_data = np.linspace(-5, 5, num=50)
y_data = 2.9 * np.sin(1.5 * x_data) + np.random.normal(size=50)

# And plot it
import matplotlib.pyplot as plt
plt.figure(figsize=(6, 4))
plt.scatter(x_data, y_data)

Now fit a simple sine function to the data

from scipy import optimize

def test_func(x, a, b):
    return a * np.sin(b * x)

params, params_covariance = optimize.curve_fit(test_func, x_data, y_data,
                                               p0=[2, 2])

print(params)

Out:

[3.05931973 1.45754553]

And plot the resulting curve on the data

plt.figure(figsize=(6, 4))
plt.scatter(x_data, y_data, label='Data')
plt.plot(x_data, test_func(x_data, params[0], params[1]),
         label='Fitted function')

plt.legend(loc='best')

plt.show()

Total running time of the script: ( 0 minutes 0.026 seconds)

Download Python source code: plot_curve_fit.py

Download Jupyter notebook: plot_curve_fit.ipynb

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