"""Ex. 5.19 from 'A primer on...'
Use numpy tools to fit polynomials to the
data read from file in 5.17. For convenience we
import the function from 5.17 and use it 
for reading the data.
"""
import numpy as np
import matplotlib.pyplot as plt
import sys
from read_density_data import read_density_data

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

if __name__ == "__main__":
    temp, dens = read_density_data(sys.argv[1])
    fit(temp,dens,[1,2])

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