convert a 2D numpy array to a 2D numpy matrix

Question

I have a python code in which I have to convert a 2D array to a 2D matrix so that I can use it to calculate inverse.For that I am using numpy.matrix(array) but it is not working. Can anyone tell how to convert a 2D array to a numpy matrix? The array consists of all float numbers

Inverse of Numpy matrix to array

Tobias Kienzler
– Tobias Kienzler

2013-07-03 08:55:14 +00:00
Commented Jul 3, 2013 at 8:55 — Tobias Kienzler
– Tobias Kienzler, Commented Jul 3, 2013 at 8:55
You can also call np.linalg.inv on the array directly.

David Zwicker
– David Zwicker

2013-07-03 10:54:11 +00:00
Commented Jul 3, 2013 at 10:54 — David Zwicker
– David Zwicker, Commented Jul 3, 2013 at 10:54

Tobias Kienzler · Accepted Answer · 2013-07-03 08:56:19Z

29

If a is your array, np.asmatrix(a) is a matrix.

answered Jul 3, 2013 at 8:56

Tobias Kienzler

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5 Comments

abcdxx Over a year ago

error File "C:\xampp\htdocs\webdev\123.py", line 47, in <module> print A.I File "C:\Python27\lib\site-packages\numpy\matrixlib\defmatrix.py", line 859, in getI return asmatrix(func(self)) File "C:\Python27\lib\site-packages\numpy\linalg\linalg.py", line 1574, in pinv u, s, vt = svd(a, 0) File "C:\Python27\lib\site-packages\numpy\linalg\linalg.py", line 1278,in svd a =_fastCopyAndTranspose(t, a) File "C:\Python27\lib\site-packages\numpy\linalg\linalg.py", line 145, in _fastCopyAndTranspose cast_arrays = cast_arrays + (_fastCT(a.astype(type)) ValueError: setting an array element with a sequence.

Tobias Kienzler Over a year ago

@abcdxx Come on, you can't just bomb me with a bunch of error messages, especially not without context. What gives you this error, what parameters did you pass to which function etc?

abcdxx Over a year ago

I hv a 2D list I converted it to array using np.array and then further calculated inverse from matrix using A.I where A=np.asmatrix(array) but it gave the above error

Tobias Kienzler Over a year ago

Why don't you convert that list directly into a matrix? Anyway, you probably should post a minimum working example in a new question about this error, if you can't find it via google.

Tobias Kienzler Over a year ago

So you got an answer there, and as you can see .asmatrix was used

Community · Accepted Answer · 2017-05-23 12:25:22Z

2

If you have a list of lists (as you mentioned), you need to convert it first to a numpy array; see how to convert 2d list to 2d numpy array?

A short example is given here:

import numpy as np
a = [[  0. +0.j,   1.j,   2. -2.j],
     [  4. -4.j,   5. -5.j,   6. -1.j],
     [  8. -8.j,   9. -9.j,  10.]]
b = np.matrix(np.array(a))
b_inv = np.linalg.inv(b)

edited May 23, 2017 at 12:25

CommunityBot

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answered Dec 18, 2014 at 9:31

strpeter

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