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MAINT: Adjust type promotion in linalg.norm #10390

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Jan 12, 2018
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MAINT: Adjust type promotion in linalg.norm #10390

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8cfc788
ENH: Preserve norm dtype for order 0
eric-wieser Jan 11, 2018
04896b0
BUG: Avoid unintentional promotion to `float`, and do ops in place fo…
eric-wieser Jan 11, 2018
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6 changes: 3 additions & 3 deletions doc/release/1.14.0-notes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -179,10 +179,10 @@ functions, and if used would likely correspond to a typo.
Previously, this would promote to ``float64`` when arbitrary orders were
passed, despite not doing so under the simple cases::

>>> f32 = np.float32([1, 2])
>>> np.linalg.norm(f32, 2.0).dtype
>>> f32 = np.float32([[1, 2]])
>>> np.linalg.norm(f32, 2.0, axis=-1).dtype
dtype('float32')
>>> np.linalg.norm(f32, 2.0001).dtype
>>> np.linalg.norm(f32, 2.0001, axis=-1).dtype
dtype('float64') # numpy 1.13
dtype('float32') # numpy 1.14

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6 changes: 4 additions & 2 deletions numpy/linalg/linalg.py
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Expand Up @@ -2277,7 +2277,7 @@ def norm(x, ord=None, axis=None, keepdims=False):
return abs(x).min(axis=axis, keepdims=keepdims)
elif ord == 0:
# Zero norm
return (x != 0).astype(float).sum(axis=axis, keepdims=keepdims)
return (x != 0).astype(x.real.dtype).sum(axis=axis, keepdims=keepdims)
elif ord == 1:
# special case for speedup
return add.reduce(abs(x), axis=axis, keepdims=keepdims)
Expand All @@ -2292,7 +2292,9 @@ def norm(x, ord=None, axis=None, keepdims=False):
raise ValueError("Invalid norm order for vectors.")
absx = abs(x)
absx **= ord
return add.reduce(absx, axis=axis, keepdims=keepdims) ** (1.0 / ord)
ret = add.reduce(absx, axis=axis, keepdims=keepdims)
ret **= (1 / ord)
return ret
elif len(axis) == 2:
row_axis, col_axis = axis
row_axis = normalize_axis_index(row_axis, nd)
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