Looks good.
On Sat, Feb 20, 2010 at 3:11 PM, Øyvind Jensen <jensen.oyv...@gmail.com>wrote:
> ---
> 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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