CODEWITHSUNDEEP
pythonnumpy
marriam nayyer
marriam nayyer

Reputation: 697

How can I take the square root of -1 using python?

When I take the square root of -1 it gives me an error:

invalid value encountered in sqrt

How do I fix that?

from numpy import sqrt
arr = sqrt(-1)
print(arr)

Upvotes: 12

Views: 34982

Answers (7)

ravikt
ravikt

Reputation: 1058

This can be done by specifying the dtype as complex in numpy's sqrt function

from numpy import sqrt
arr = sqrt(-1, dtype=np.complex128)
print(arr)

Upvotes: 0

David Zwicker
David Zwicker

Reputation: 24338

I just discovered the convenience function numpy.emath.sqrt explained in the sqrt documentation. I use it as follows:

>>> from numpy.emath import sqrt as csqrt
>>> csqrt(-1)
1j

Upvotes: 21

mnuizhre
mnuizhre

Reputation: 169

The latest addendum to the Numpy Documentation here, adds the command numpy.emath.sqrt which returns the complex numbers when the negative numbers are fed to the square root sign in a operation.

Upvotes: 1

John La Rooy
John La Rooy

Reputation: 304503

You need to use the sqrt from the cmath module (part of the standard library)

>>> import cmath
>>> cmath.sqrt(-1)
1j

Upvotes: 12

hobenkr
hobenkr

Reputation: 1234

Others have probably suggested more desirable methods, but just to add to the conversation, you could always multiply any number less than 0 (the value you want the sqrt of, -1 in this case) by -1, then take the sqrt of that. Just know then that your result is imaginary.

Upvotes: 0

Warren Weckesser
Warren Weckesser

Reputation: 114976

To avoid the invalid value warning/error, the argument to numpy's sqrt function must be complex:

In [8]: import numpy as np

In [9]: np.sqrt(-1+0j)
Out[9]: 1j

As @AshwiniChaudhary pointed out in a comment, you could also use the cmath standard library:

In [10]: cmath.sqrt(-1)
Out[10]: 1j

Upvotes: 36

Marcin
Marcin

Reputation: 49886

The square root of -1 is not a real number, but rather an imaginary number. IEEE 754 does not have a way of representing imaginary numbers.

numpy has support for complex numbers. I suggest you use that: http://docs.scipy.org/doc/numpy/user/basics.types.html

Upvotes: 0

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