#!/usr/bin/env python
# -*- coding: utf-8 -*- 
'''
Este trabalho está licenciado sob a Licença Creative Commons 
Atribuição-CompartilhaIgual 4.0 Internacional. Para ver uma cópia desta licença,
visite https://creativecommons.org/licenses/by-sa/4.0/ ou envie uma carta 
para Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
'''

from __future__ import division
from math import *
import matplotlib.pylab as plt
import numpy as np

fig = plt.figure(figsize = (4,4), dpi=100, frameon=False)
ax = plt.subplot(1,1,1)
plt.axis('off')

#x - axis
ax.set_xlim((-1,5))
plt.arrow(-1,0,6,0,head_width=0.1, length_includes_head=True, facecolor='black')
plt.text(4.7, -0.3, r'$x$', fontsize=14)

#y- axis
ax.set_ylim((-1,5))
plt.arrow(0,-1,0,6,head_width=0.1, length_includes_head=True, facecolor='black')
plt.text(-0.3, 4.7, r'$y$', fontsize=14)

#arbritary function
def fun(x):
    return 3.5*np.sin(x/2)
plt.text(3,4,'$y=f(x)$', fontsize=14)

xx = np.linspace(0.5,4)
plt.plot(xx,fun(xx))

#arbritary point at domain
a = 2.5
plt.plot([a,a], [-0.075, fun(a)], 'k--')
plt.text(a-0.1, -0.3, '$a$', fontsize=14)
plt.plot(a, fun(a), 'ko', markersize=4)
plt.plot([-0.075,a], [fun(a), fun(a)], 'k--')
plt.text(-0.8, fun(a)-0.1, '$f(a)$', fontsize=14)



plt.savefig('Graph_of_a_function.svg', bbox_inches='tight', pad_inches=0.0)