feat: Kronecker delta sums#975
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| /-- The Kronecker delta function, `ite (i = j) 1 0`. -/ | ||
| def kroneckerDelta [Ring R] (i j : Fin d) : R := if (i = j) then 1 else 0 | ||
| def kroneckerDelta (i j : Fin d) : ℝ := if (i = j) then 1 else 0 |
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I'm not sure this is a good idea, if anything we'd want to generalize this definition further and not narrow the uses. Can you explain why you want to revise the definition in this way?
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No good reason - I've reverted to a general ring. Are the newly added simp lemmas the best way to handle coercion? (I have ℝ → ℂ separate because for some reason ℝ is not a subring of ℂ...!)
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In making these changes a few commutator proofs broke in Commutation.lean and LaplaceRungeLenzVector.lean; I have fixed those which had a quick solution and replaced those which are more computation-heavy with sorries. I will simplify / golf these two files soon.