8000 Added an 'elementary' function. by mttpgn · Pull Request #4573 · numpy/numpy · GitHub
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Added an 'elementary' function. #4573

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Added an 'elementary' function. #4573

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f9cb6cb
Added an 'elementary' function.
Mar 31, 2014
159b9ae
Update twodim_base.py
mttpgn Apr 1, 2014
0e10a44
Tightened up code per github suggestions.
Apr 9, 2014
e4e3ca1
Merge branch 'master' of https://github.com/mttp/numpy
Apr 9, 2014
c3f45d3
Stopped using np.matrix, brought back the swap variable.
Apr 10, 2014
9dba261
Added tests for the elementary function.
Apr 14, 2014
1da28fd
Added 'elementary' to __all__
Apr 14, 2014
4de601b
Tests for 'elementary' should inherit TestCase.
Apr 14, 2014
08965f5
Eliminated the swap variable correctly.
Apr 14, 2014
480c51b
Tests need to call np.elementary rather than elementary.
Apr 14, 2014
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Tightened up code per github suggestions.
  • Loading branch information
Matt Pagan committed Apr 9, 2014
commit 0e10a449ee2c483594d4d1303f0313eba91b9ae5
41 changes: 21 additions & 20 deletions numpy/lib/twodim_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1000,22 +1000,22 @@ def triu_indices_from(arr, k=0):
return triu_indices(arr.shape[-2], k=k, m=arr.shape[-1])


def elementary(N, i, j=None, t=None, dtype=float):
def elementary(N, i, j=None, multiplier=None, dtype=float):
"""
Return an array arranged like an elementary matrix.

Parameters
----------
N : int
The size of the NxN array to be returned. Elementary matrices
are be square.
are square by definition.
i : int
The index of the first row on which operations are to be
performed.
j : int
If set, the index of the second row on which operations are to
be performed.
t : scalar
multiplier : scalar
If set, the factor by which a given row will be multiplied.

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Any reason not to document the dtype arg?

Returns
Expand All @@ -1028,8 +1028,12 @@ def elementary(N, i, j=None, t=None, dtype=float):
--------
eye, identity

Notes
-----
This function's primary utility is in matrix multiplication.

Examples
-------
--------
To swap the the first and third rows of a 4x4 identity matirx:

>>> L = elementary(4, 0, 2)
Expand All @@ -1046,7 +1050,7 @@ def elementary(N, i, j=None, t=None, dtype=float):
[11, 13, 17, 19],
[23, 29, 31, 37],
[41, 43, 47, 53]])
>>> L*H
>>> L * H
matrix([[ 23., 29., 31., 37.],
[ 11., 13., 17., 19.],
[ 2., 3., 5., 7.],
Expand All @@ -1056,7 +1060,7 @@ def elementary(N, i, j=None, t=None, dtype=float):
multiplication takes place in reverse order), the result is the
given matrix with its first and third columns swapped.

>>> H*L
>>> H * L
matrix([[ 5., 3., 2., 7.],
[ 17., 13., 11., 19.],
[ 31., 29., 23., 37.],
Expand All @@ -1070,13 +1074,13 @@ def elementary(N, i, j=None, t=None, dtype=float):
[11, 13, 17, 19],
[23, 29, 31, 37],
[41, 43, 47, 53]])
>> M=elementary(4, 1, 3, 10000, int)
>> M = elementary(4, 1, 3, 10000, int)
>> M
array([[ 1, 0, 0, 0],
[ 0, 1, 0, 0],
[ 0, 0, 1, 0],
[ 0, 10000, 0, 1]])
>> M*H
>> M * H
matrix([[ 2, 3, 5, 7],
[ 11, 13, 17, 19],
[ 23, 29, 31, 37],
Expand All @@ -1089,7 +1093,7 @@ def elementary(N, i, j=None, t=None, dtype=float):
[11, 13, 17, 19],
[23, 29, 31, 37],
[41, 43, 47, 53]])
>>> H*elementary(len(H), len(H)-1, t=2)
>>> H * elementary(len(H), len(H)-1, multiplier=2)
matrix([[ 2., 3., 5., 14.],
[ 11., 13., 17., 38.],
[ 23., 29., 31., 74.],
Expand All @@ -1099,18 +1103,15 @@ def elementary(N, i, j=None, t=None, dtype=float):
of elementary matrices.

"""
m=eye(N, dtype=dtype)
if j==None and t==None:
raise ValueError("One or more of {0} and {1} must be set.".format( \
'j', 't'))
elif t==None:
swap = array(m[i])
m[i] = m[j]
m[j] = swap
m = eye(N, dtype=dtype)
if j is None and multiplier is None:
raise ValueError("One or more of 'j' and 'multiplier' must be set.")
elif multiplier is None:
m[i], m[j] = m[j], m[i]
return m
elif j==None:
m[i] *= t
elif j is None:
m[i] *= multiplier
return m
else:
m[j] += (t * m[i])
m[j] += (multiplier * m[i])
return m
0