import numpy as np
import matplotlib.pyplot as plt
import math


# make an x axis from -5 to 5 with 100 grid points
x_coords = np.linspace(-5,5,100)
y_coords = np.linspace(-5,5,100)

X , Y = np.meshgrid(x_coords,y_coords)

#define constants for formula
permitivity= 8.85 * 10**-12
k = 1.0 / (4.0 * math.pi * permitivity)
q = 1.0 * 10**-9
charge_location = np.array([0,0])


def calc_efield (x_coord,y_coord):

    # declare two element vector for the r_vector
    r_vector = np.array([0,0])

    # calculate r vector by subtracting x coords and y coords
    r_vector[0] = x_coord - charge_location[0]
    r_vector[1] = y_coord - charge_location[1]

    #find the magnitude of the vector
    r_mag = np.linalg.norm(r_vector)

    #calculate the kq/r^2 part
    constant = k*q / r_mag ** 2

    #calculate the unit vector as the r_vector over its magnitude
    unit_vector = r_vector
    unit_vector = unit_vector / r_mag

    #calculate the electric field by multiplying the constant part with the unit vector
    e_field = unit_vector
    e_field = e_field * constant


    return e_field