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st: RE: RE: Bessel
Recall that in Stata pi = 3.14159... is accessible to machine precision
as either _pi or c(pi). So there is no harm done,
and possibly some small harm avoided, in using those
inbuilt constants directly.
> I found an approximation to the Bessel Type 2 in an old
> journal article.
> Since it is an approximation anyhow, I further simplified it
> by calculating pi/2
> and pi/4 to their numeric values (to 4 decimal points),
> which are 1.5708 and
> 0.7854 respectively. The actual approximation I found was given as:
> J_n(x) ~ sqrt(2/(pi*x)) * sin(x-(2*n+1)*(pi/4).
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