Inverse of a matrix using numpy

Question

I d like to use numpy to calculate the inverse   But I m getting an error     numpy ndarry  object has no attribute I   To calculate inverse of a matrix in numpy  say matrix M  it should be simply  print M I   Here s the code   x   numpy empty  3 3   dtype int  for comb in combinations with replacement range 10   9      x flat      comb    print x I   I m presuming  this error occurs because x is now flat  thus  I  command is not compatible  Is there a work around for this   My goal is to print the INVERSE MATRIX of every possible numerical matrix combination

User · Answer

Another way to do this is to use the numpy matrix class  rather than a numpy array  and the I attribute  For example    gt  gt  gt  m   np matrix   2 3   4 5     gt  gt  gt  m I matrix   -2 5   1 5            2    -1

User · Answer

What about inv   e g       my inverse array   inv my array

User · Answer

Inverse of a matrix using python and numpy    gt  gt  gt  import numpy as np  gt  gt  gt  b   np array   2 3   4 5     gt  gt  gt  np linalg inv b  array   -2 5   1 5            2    -1        Not all matrices can be inverted  For example singular matrices are not Invertable    gt  gt  gt  import numpy as np  gt  gt  gt  b   np array   2 3   4 6     gt  gt  gt  np linalg inv b   LinAlgError  Singular matrix   Solution to singular matrix problem   try-catch the Singular Matrix exception and keep going until you find a transform that meets your prior criteria AND is also invertable    Intuition for why matrix inversion can t always be done  like in singular matrices   Imagine an old overhead film projector that shines a bright light through film onto a white wall   The pixels in the film are projected to the pixels on the wall     If I stop the film projection on a single frame  you will see the pixels of the film on the wall and I ask you to regenerate the film based on what you see   That s easy  you say  just take the inverse of the matrix that performed the projection   An Inverse of a matrix is the reversal of the projection   Now imagine if the projector was corrupted  and I put a distorted lens in front of the film   Now multiple pixels are projected to the same spot on the wall   I asked you again to  undo this operation with the matrix inverse    You say   I can t because you destroyed information with the lens distortion  I can t get back to where we were  because the matrix is either Singular or Degenerate    A matrix that can be used to transform some data into other data is invertable only if the process can be reversed with no loss of information   If your matrix can t be inverted  perhaps you are defining your projection using a guess-and-check methodology rather than using a process that guarantees a non-corrupting transform   If you re using a heuristic or anything less than perfect mathematical precision  then you ll have to define another process to manage and quarantine distortions so that programming by Brownian motion can resume   Source    http   docs scipy org doc numpy reference generated numpy linalg inv html numpy linalg inv

User · Answer

The I attribute only exists on matrix objects  not ndarrays  You can use numpy linalg inv to invert arrays   inverse   numpy linalg inv x    Note that the way you re generating matrices  not all of them will be invertible  You will either need to change the way you re generating matrices  or skip the ones that aren t invertible   try      inverse   numpy linalg inv x  except numpy linalg LinAlgError        Not invertible  Skip this one      pass else        continue with what you were doing   Also  if you want to go through all 3x3 matrices with elements drawn from  0  10   you want the following   for comb in itertools product range 10   repeat 9     rather than combinations with replacement  or you ll skip matrices like  numpy array   0  1  0                 0  0  0                 0  0  0

[python] Inverse of a matrix using numpy

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