# What is curve fit in Python?

Curve fitting is a method which is used to fit parameters to data points . For example , you can initialize a parameter for a software code and run it to find the correct parameters for the equation. Python provides a very compact way to perform this task using scipy.optimize.curve_fit.

• To get started, let’s create a data sequence as a numpy array and use it in our computation. The function np.arange(100) generates aarray from 0 to 100 with 10 elements.
• Having the data set, we can write a function to calculate the parameter value from the data set.we will use y = a * x^2 function for this example.
`def y_by_x(x):  a = 1 xdata = np.arange(x, 100) return a * x**2`

Now, we are ready to use the function as an input for scipy optimize.curve_fit which will calculate the parameter values. You can pass many parameters as input for this function as shown below.

`from __future__ import print_function from math import * from scipy.optimize import curve_fit import numpy as np def y_by_x(x):  a = 1         x    = np.arange(x, 100) return a * x**2 ''' Define the dataset ''' d = np.arange(100) # Generate the array  # x and y are 2 variables to be fitted  # a and b are the parameters of interest to us ''' Define the objective function ''' '''''''''''''''' '''Evaluate the objective function ''' '''Önderstand the Gradient of Objective Function ''' '''Setup the Parameters ''' ''''''''''''''''    ''' '''Fit the Curve ''' '''''''''''''''''''' '''Plot the Results ''' ''']]>까пїх дэглэх  `

The first line defines thefunction y_by_x which accepts one argument x. Next, we define the data set as d with the range(100). The x and y are the variables to be fitted where y is a function of x. The last line defines a and b which will be the parameters to be optimized. You can define many input parameters such as chi2, rtol, atol and constraints depending on your requirements. Here, we are just showing a simple case with fixed values for chi2, rtol, atol and constraints as None. The“сё„” in the output is due to a bug in Python.

Scipy Curve Fit Report

If you try to run the code, you will get an error as “NameError: name ‘a’ is not defined”. This is because we have passed the function y_by_x for calculating a and b as arguments. However, thea is not defined in the _by_x_ function. You should fix the error by changing the variable name to ‘a’ and run the test case again. Once the process is complete, you will see the report as below. The returned values are the coefficients a, b and chi2. The rsquared value is 0.992 which is a very goodfit. The p value of the chi2 is 0.2143 which tells us there is 0.2143% chance that the obtained values have a better fit than the one calculated from random points. For more example on how to get started with this function, readthe official documentation.

The report shows 2 arrays. The first one is x_data which is a 2-element array with the first element as the starting index and the second as the count of the elements in the y column. The second one is y which is our result set. The results are returned asa tuple containing (a, b, c2). To see the detailed explanation of the arguments, see the reference documentation about “scipy.optimize.curve_fit” that you can find here.

Scipy Optimize Curve Fit Documentation

## Additional Question – What is curve fit in Python?

### How do you fit a curve to data in Python? :

Curve_fit from Scipy should be imported for data fitting. Organize your independent variable (your x values) as a list or numpy array. List your dependent variables’ numpy arrays (your y values) in a list format. For the equation you want to fit, create a function. To fit your data, use the curve_fit function.