 Integer-order Bessel reflection identity (source code)

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= Integer-order Bessel reflection identity
{c}
{title2=$J_{-m}(z)=(-1)^mJ_m(z)$}

For integer $m\geq0$, $J_{-m}(z)=(-1)^mJ_m(z)$. Thus negative integer orders remain regular at zero. The familiar $J_m(z)\sim z^m/(2^mm!)$ formula is used for nonnegative order; a negative factorial is not a valid continuation.

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