# -*- coding: utf-8 -*-
#from __future__ import unicode_literals
#import matplotlib.pyplot as plt
#from sympy import symbols, sqrt
#from sympy.plotting import plot

#http://www.scipy-lectures.org/intro/matplotlib/matplotlib.html

import numpy as np
import matplotlib.pyplot as plt
#x,y = symbols('x,y')
#y = sqrt(64-x**2)

#title="$y=\sqrt{64-x^2}$"
#graph = plot((y),(x,-10,10),(y,-1,12),ylabel='$y$',xlabel="$y=\sqrt{64-x^2}$", show=True)

plt.rc('text', usetex=True)
plt.rc('font', family='serif')

X = np.linspace(-8, 8, 512, endpoint=True)

C, S = np.cos(X), np.sin(X)

Y=np.sqrt(64-X**2)

#plt.plot(X, C)

#plt.figure(figsize=(5, 5), dpi=600)
plt.ylim(Y.min() * 1.1, Y.max() * 1.1)
plt.xlim(X.min() * 1.1, X.max() * 1.1)

ax = plt.gca()  # gca stands for 'get current axis'
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
ax.xaxis.set_ticks_position('bottom')
ax.spines['bottom'].set_position(('data',0))
ax.yaxis.set_ticks_position('left')
ax.spines['left'].set_position(('data',0))

#x
plt.arrow(8.5, -0.003, 0.1, 0, head_width=0.1, head_length=0.25,clip_on=False) #width=0.015, color="k", clip_on=False, head_width=0.12, head_length=0.22)

#y
plt.arrow(0.0, 8.7, 0, 0.1, clip_on=False, head_width=0.1, head_length=0.25)


plt.yticks([2,4,6,8])
plt.xticks([-8,-6,-4,-2,0,2,4,6,8])#),rotation='vertical')

plt.margins(0.2)


plt.plot(X, Y, color="slateblue")

plt.title(r"$\displaystyle y=\sqrt{64-x^2}$" ,fontsize=12, color='slateblue',y=0.15,x=0.3)

#plt.show()
#graph.save('plot06a.png')

plt.savefig('plot06a.pdf', dpi=600)