1.7 Getting started with the NumPy library
① Random Array
>>> from numpy import*
>>> random.rand(4,4)
array([[ 0.43831197, 0.35192743, 0.41718421, 0.02885252],
[ 0.38820193, 0.6842994 , 0.56657079, 0.6378907 ],
[ 0.7795009 , 0.67264657, 0.84689064, 0.38003772],
[ 0.15846023, 0.42460139, 0.60844758, 0.88809248]])
②Convert an array to a matrix
>>> randMat = mat(random.rand(4,4))
>>> invRandMat = randMat.I
The ".I" operator solves the inverse of a matrix.
>>> randMat
matrix([[ 0.96119052, 0.65586165, 0.9050705 , 0.82003587],
[ 0.09912414, 0.27526886, 0.04278784, 0.53352162],
[ 0.43153359, 0.89609418, 0.70573325, 0.4582519 ],
[ 0.10391469, 0.92706015, 0.47706808, 0.16927545]])
>>> randMat.I
matrix([[ 8.78378885, -0.24249478, -20.47960842, 13.65333088],
[ 3.84524822, 0.61977968, -10.7757186 , 8.59005951],
[ -8.3398511 , -1.76950141, 22.72457239, -15.53996251],
[ -2.94705669, 1.74153052, 7.54216509, -5.7224096 ]])
>>> randMat*invRandMat
matrix([[ 1.00000000e+00, -3.41706192e-17, -5.84419709e-16,
3.03544577e-15],
[ 1.17655922e-16, 1.00000000e+00, -1.16736773e-15,
9.32123779e-16],
[ -7.81192093e-16, -6.74387259e-17, 1.00000000e+00,
-1.49237318e-15],
[ -3.48749572e-16, 4.46109067e-17, -1.61100173e-15,
1.00000000e+00]])
>>> myEye=randMat.I*invRandMat
>>> myEye - eye(4)
matrix([[ 205.78223862, 57.73607224, -539.69016914, 357.9673263 ],
[ 100.7115514 , 32.47917437, -265.51369969, 176.12281464],
[-223.78206269, -66.34881268, 588.06576143, -393.27984115],
[ -65.22597483, -21.51761168, 169.82144272, -110.73628032]])
The function eye(4) just creates an identify matrix of size 4.
