"""
Ex 6.18 from A Primer on ...
Use polyfit from numpy to fit a polynomial
to data points read from a file.

We reuse the function for reading the
file from Ex 5.16.
"""

import numpy as np
import matplotlib.pyplot as plt
#import sys

from read_density_data import read_data

def fit(x,y,deg):
    for d in deg:
        coeff = np.polyfit(x,y,d)
        p = np.poly1d(coeff)
        plt.plot(x,p(x),label=f'degree = {d}')
    plt.plot(x,y,'ro',label ='data')
    plt.legend()
    plt.show()

temp, dens = read_data('density_water.txt')

fit(temp,dens, [1,2])

"""
Terminal>python fit_density_data.py
(output is a plot)
"""