# -*- coding: utf-8 -*-
# numpytest1.py 

import numpy as np

x = np.array([1,2,3,4]); 
y= np.array([5,6,7,8]); 
z= np.array([10,20])
print(x)
print(x*y)
print(x + 4)
# print(x+z)  # 에러

#=======================================================

print(np.arange(3))
print(np.arange(3.0, 7.0))
print(np.arange(3.1, 4.5, 0.5))

print(np.linspace(2.0, 3.0, num=5))
print(np.linspace(2.0, 3.0, num=5, retstep=True)) 

#=====================================================

A = np.array( [[1,1], [0,1]] )
B = np.array( [[2,0], [3,4]] )

print(A, B)
print(A[0,1])
print(A * B)                       # elementwise product
print(A @ B)                       # matrix product
print(A.dot(B))                  # another matrix product

#======================================================

print(np.ones(5))
print(np.zeros(4))
J = np.ones([5,5])
print('J: ', J)
myones = np.ones([5,1])
print('Jx1: ', J @ myones)
print('Jx1: ', J.dot(myones))


#======================================================

a1 = np.empty((2,3), dtype=int)
print(a1)
print(a1.shape)
a2 = a1.reshape(3,2)
print(a2)
print('행의 수: ', a2.shape[0])