From: Fabian Seoane <fab...@fseoane.net>
Added test and docs
---
sympy/functions/elementary/complexes.py | 19 ++++++++++++++++---
sympy/functions/elementary/tests/test_complexes.py | 6 +++++-
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/sympy/functions/elementary/complexes.py
b/sympy/functions/elementary/complexes.py
index 2e94716..250d808 100644
--- a/sympy/functions/elementary/complexes.py
+++ b/sympy/functions/elementary/complexes.py
@@ -193,6 +193,20 @@ def _eval_is_zero(self):
return (self[0] is S.Zero)
class abs(Function):
+ """Return the absolute value of the argument. This is an extension of the
built-in
+ function abs to accept symbolic values
+
+ Examples
+
+ >>> from sympy import abs, Symbol
+ >>> abs(-1)
+ 1
+ >>> x = Symbol('x', real=True)
+ >>> abs(-x)
+ abs(x)
+ >>> abs(x**2)
+ x**2
+ """
nargs = 1
@@ -228,9 +242,8 @@ def eval(cls, arg):
return sqrt( (arg * arg.conjugate()).expand() )
if arg.is_Pow:
base, exponent = arg.as_base_exp()
- if exponent.is_Number:
- if exponent.is_even:
- return arg
+ if exponent.is_even and base.is_real:
+ return arg
return
@classmethod
diff --git a/sympy/functions/elementary/tests/test_complexes.py
b/sympy/functions/elementary/tests/test_complexes.py
index 8227cc4..28d97a9 100644
--- a/sympy/functions/elementary/tests/test_complexes.py
+++ b/sympy/functions/elementary/tests/test_complexes.py
@@ -98,14 +98,18 @@ def test_abs():
assert x**(2*n) == abs(x)**(2*n)
def test_abs_real():
+ # test some properties of abs that only apply
+ # to real numbers
x = Symbol('x', complex=True)
assert sqrt(x**2) != abs(x)
+ assert abs(x**2) != x**2
+
x = Symbol('x', real=True)
assert sqrt(x**2) == abs(x)
+ assert abs(x**2) == x**2
def test_abs_properties():
x = Symbol('x')
-
assert abs(x).is_real == True
assert abs(x).is_positive == None
assert abs(x).is_nonnegative == True
--
1.6.1.2
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