Re: Array multiplication: implicit loop query

[billb(at)attinet.com (Bill B.)]

george@apg.ph.ucl.ac.uk (george Millward) wrote in message news:<d90c0773.0108100256.6398a693@posting.google.com>...
> Hi there
> 
> I was just calculating the following equation:
> 
> DEN_H = MMR_H * Pres * RMT / ( atomic_mass_H * Gas_constant * TN )
> 
> These  numbers are 3D arrays, 1D arrays and constants, i.e.,
> 
> MMR_H = fltarr(30,91,40)
> Pres = fltarr(30)
> RMT = fltarr(30,91,40)
> atomic_mass_H = constant
> Gas_constant  = constant
> TN =fltarr(30,91,40)
> 
> The result of this is DEN_H (previously undefined) which ends up being
> fltarr(30) - i.e., 1 dimensional.
> To my mind DEN_H should be 3D (30,91,40) - shouldn't it ?  Doesn't IDL
> understand that I am implicity doing a full 3D calculation here ?  

No.

> It
> would seem that, to get this to work I need to make
> Pres=fltarr(30,91,40). 

Yes.

IDL> a = indgen(20,20)
IDL> b = indgen(20)
IDL> c = b * a
IDL> help, c
C               INT       = Array[20]

I believe you need to REPLICATE 'Pres' as needed.


-Bill B.