# forelse.py
# Author: Alex Gezerlis
# Numerical Methods in Physics with Python (2nd ed., CUP, 2023)

def look(target,names):
    for name in names:
        if name==target:
            val = name
            break
    else:
        val = None
    return val

names = ["Alice", "Bob", "Eve"]
print(look("Eve", names))
print(look("Jack", names))

# plotex.py
# Author: Alex Gezerlis
# Numerical Methods in Physics with Python (2nd ed., CUP, 2023)

import matplotlib.pyplot as plt

def plotex(cxs,cys,dxs,dys):
    plt.xlabel('x', fontsize=20)
    plt.ylabel('f(x)', fontsize=20)
    plt.plot(cxs, cys, 'r-', label='one function')
    plt.plot(dxs, dys, 'b--^', label='other function')
    plt.legend()
    plt.show()

cxs = [0.1*i for i in range(60)]
cys = [x**2 for x in cxs]
dxs = [i for i in range(7)]
dys = [x**1.8 - 0.5 for x in dxs]

plotex(cxs, cys, dxs, dys)

# vectorfield.py
# Author: Alex Gezerlis
# Numerical Methods in Physics with Python (2nd ed., CUP, 2023)

import numpy as np
import matplotlib.pyplot as plt
from math import sqrt
from copy import deepcopy

def makefield(xs, ys):
    qtopos = {1: (-1,0), -1: (1,0)}
    n = len(xs)
    Exs = [[0. for k in range(n)] for j in range(n)]
    Eys = deepcopy(Exs)
    for j,x in enumerate(xs):
        for k,y in enumerate(ys):
            for q,pos in qtopos.items():
                posx, posy = pos
                R = sqrt((x - posx)**2 + (y - posy)**2)
                Exs[k][j] += q*(x - posx)/R**3
                Eys[k][j] += q*(y - posy)/R**3
    return Exs, Eys

def plotfield(boxl,n):
    xs = [-boxl + i*2*boxl/(n-1) for i in range(n)]
    ys = xs[:]
    Exs, Eys = makefield(xs, ys)
    xs=np.array(xs); ys=np.array(ys)
    Exs=np.array(Exs); Eys=np.array(Eys)
    plt.streamplot(xs, ys, Exs, Eys, density=1.5, color='m')
    plt.xlabel('$x$')
    plt.ylabel('$y$')
    plt.show()

plotfield(2.,20)