"""
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

"""
Make sure the file read_density_data.py
exists in the same directory as the current file.
"""
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)
        y_poly = p(x)
        plt.plot(x,y_poly)
    plt.plot(x,y,'ro')
    plt.show()

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

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

"""
Terminal> python fit_density_data.py
Output is a plot
"""