How do I create a negated matrix? (Python)

Question

Let's say I have a matrix [[-2,4],[-6,8]].

I want to know how to get the opposite of those numbers: [[2,-4],[6,-8]].

Is there a special function in Python I'm supposed to use?

If you're doing linear algebra in Python, use numpy. – Emmet Apr 04 '14 at 19:16 — Emmet, Apr 04 '14 at 19:16

score 3 · Answer 1 · answered Apr 04 '14 at 19:16

3

numpy is awesome :P

a = numpy.array( [[-2,4],[-6,8]])
a *= -1
print a

answered Apr 04 '14 at 19:16

Joran Beasley

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why not simply `a = -a` ? – lejlot Apr 04 '14 at 19:29
Is there a way to do it Without numpy? I'd prefer not using packages. – user2581724 Apr 04 '14 at 19:33
@shaktimaan's answer covers doing it without numpy ... but really numpy is an amazing package – Joran Beasley Apr 04 '14 at 19:35
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You can just do: `a = -numpy.array( [[-2,4],[-6,8]])` – jterrace Apr 04 '14 at 19:54

score 1 · Answer 2 · edited Apr 04 '14 at 19:30

1

Using a list comprehension is one way to go about it:

>>> data = [[-2,4],[-6,8]]
>>> [[-ele for ele in item] for item in data]
[[2, -4], [6, -8]]

edited Apr 04 '14 at 19:30

anon582847382

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answered Apr 04 '14 at 19:15

shaktimaan

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score 0 · Answer 3 · 2014-04-04T19:33:51.127

0

import numpy

matrix = numpy.array([[-2,4],[-6,8]])
negatedMatrix = matrix * -1

print negatedMatrix

Giving the output:

[[ 2 -4]
 [ 6 -8]]

edited Apr 04 '14 at 19:33

answered Apr 04 '14 at 19:24

skamsie · Answer 4 · 2014-04-04T19:52:33.647

0

If you do not want to import packages and you also have a problem with list comprehensions but you like unnecessary complicated things you can use map() and lambda like this:

data = [[-2,4],[-6,8]]
reversed_data = map(lambda sublist: map(lambda x: -x, sublist), data)
# [[2, -4], [6, -8]]

EDIT: This example is working in python 2.7. In python 3+ map() returns an iterator so you need to do list(map()) to get this result. (credit goes to SethMMorton)

edited Apr 04 '14 at 19:52

answered Apr 04 '14 at 19:43

skamsie

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Note that in python3 `map` returns a *map object*, so you'd have to do `list(map())` to get this result in that case. – SethMMorton Apr 04 '14 at 19:45

How do I create a negated matrix? (Python)

4 Answers4