[Getdp] $X and X[]

Tue Jul 12 19:54:38 CEST 2011

Hi folks,

I was just wondering what the difference is between $X and X[] (Y, and Z also)?

I see that $X is the current x co-ordinate, and $XS is the source x
co-ordinate.  X[] is just described as the x co-ordinate.

If I set up a perfectly symmetrical problem, then $X works fine... I'm
evaluating prob[] = exp(-1*( ($X - X0)^2 + ($Y - Y0)^2)) and integrating
within an area.  So in this case, if I set X0 = +- 1; Y0 = +- 1 , and
integrate within a unit square centred at the origin then all is well.

However as soon as any asymmetry is introduced it all goes to pot.  There is
no such problem with X[].

What's the difference between the variables?

Kind regards,

Mike Grant.
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