mul=np.array([[ 2.79358336e-03, -4.33801272e-03,  1.49405606e-01, -1.49494674e-01],
  [-4.33801272e-03,  6.73628032e-03, -2.32004399e-01,  2.32142708e-01],
  [ 1.49405606e-01, -2.32004399e-01,  7.99047014e+00, -7.99523365e+00],
  [-1.49494674e-01,  2.32142708e-01, -7.99523365e+00 , 8.00000000e+00]])
我算出来的逆矩阵是:
ni=[[1.15688790e+09 8.31687162e+08 6.45472327e+08 6.42572567e+08]
  [8.31687176e+08 2.31447075e+09 1.72043424e+09 1.66778988e+09]
  [6.45472390e+08 1.72043428e+09 5.47332438e+09 5.43220196e+09]
  [6.42572630e+08 1.66778992e+09 5.43220196e+09 5.39257748e+09]]
然后，print(np.dot(mul,ni)) 结果是：
[[  0.9793222   -0.3413915   -0.14888251  -0.32711732]
  [  0.0321095    1.53012961   0.23119211   0.5079639 ]
  [ -1.10588455 -18.25820923  -6.96250153 -17.49479675]
  [  1.10654449  18.26909256   7.96724701  18.50522614]]
这个根本不是单位阵啊。怎么回事呢？
但是，我用print(np.dot(mul,np.linalg.inv(mul)))，能得到单位阵：
[[ 1.00000000e+00  0.00000000e+00  0.00000000e+00 -1.19209290e-07]
  [-2.98023224e-08  1.00000006e+00 -2.38418579e-07  0.00000000e+00]
  [ 9.53674316e-07 -1.90734863e-06  1.00000000e+00  7.62939453e-06]
  [ 0.00000000e+00  0.00000000e+00  0.00000000e+00  1.00000000e+00]]
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