---
sympy/physics/secondquant.py | 25 +++++++++++++------------
1 files changed, 13 insertions(+), 12 deletions(-)
diff --git a/sympy/physics/secondquant.py b/sympy/physics/secondquant.py
index edc9987..687bf9d 100644
--- a/sympy/physics/secondquant.py
+++ b/sympy/physics/secondquant.py
@@ -2325,10 +2325,15 @@ def evaluate_deltas(e):
imply a loss of information, nothing is done.
In case an index appears in more than one KroneckerDelta, the resulting
- final substitution depends on the larger expression. Behavior of
- evaluate_deltas is in that case undefined.
+ substitution depends on the order of the factors. Since the ordering is
platform
+ dependent, the literal expression resulting from this function may be hard
to
+ predict.
+
+ Examples:
+ =========
+
+ We assume that
- Examples: We assume that
>>> from sympy import symbols, Function
>>> from sympy.physics.secondquant import evaluate_deltas, KroneckerDelta
>>> i,j = symbols('ij',below_fermi=True, dummy=True)
@@ -2338,9 +2343,9 @@ def evaluate_deltas(e):
>>> t = Function('t')
The order of preference for these indices according to KroneckerDelta is
- (a,b,i,j,p,q) So we get
+ (a,b,i,j,p,q).
- ==Trivial cases===
+ Trivial cases:
>>> evaluate_deltas(KroneckerDelta(i,j)*f(i)) # d_ij f(i) -> f(j)
f(_j)
@@ -2353,8 +2358,7 @@ def evaluate_deltas(e):
>>> evaluate_deltas(KroneckerDelta(q,p)*f(q)) # d_qp f(q) -> f(p)
f(_p)
-
- ==more interesting cases===
+ More interesting cases:
>>> evaluate_deltas(KroneckerDelta(i,p)*t(a,i)*f(p,q))
f(_i, _q)*t(_a, _i)
@@ -2363,16 +2367,13 @@ def evaluate_deltas(e):
>>> evaluate_deltas(KroneckerDelta(p,q)*f(p,q))
f(_p, _p)
-
- == Do nothing to prevent loss of information ===
+ Finally, here are some cases where nothing is done, because that would
+ imply a loss of information:
>>> evaluate_deltas(KroneckerDelta(i,p)*f(q))
KroneckerDelta(_i, _p)*f(_q)
-
>>> evaluate_deltas(KroneckerDelta(i,p)*f(i))
KroneckerDelta(_i, _p)*f(_i)
-
-
"""
--
1.6.5
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