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.
