***********
* Name:    emask.gs
* Purpose: creates a mask for selecting or deselecting individual ensemble
*          members; modified from Wesley Ebisuzaki's monmask.gs (v1.0.1) 
*          Defines a mask ("emask") where the n'th ensemble member is set to one
*          and the others are undefined and a second mask ("emaskinv") where the
*          nth ensemble member is set to undefined and the others to 1.
* Version: 1.0, Fri Dec 10 15:44:36 FLEST 2010
* Author:  Stefan Fronzek, stefan(dot)fronzek(at)ymparisto(dot)fi
***********
function emask(arg)

if (arg = '' | arg <= 0)
   say 'emask.gs - creates a mask for selecting or deselecting individual ensemble'
   say '           members; modified from Wesley Ebisuzaki"s monmask.gs (v1.0.1)'
   say '           Defines a mask ("emask") where the nth ensemble member is set to one'
   say '           and the others are undefined and a second mask ("emaskinv") where the'
   say '           nth ensemble member is set to undefined and the others to 1.'
   say 'Usage: run emask {e}'
   say '  e - ensemble member in the e-dimension'
   say 'Example: in a 10-member ensemble, deselect a member when calculating averages'
   say '    set lat 40'
   say '    set lon -90'
   say '    set e 1 10'
   say '    run emask 5'
   say '    set e 1'
   say '    display ave(expression*emaskinv,e=1,e=10)'
   exit
endif

monm1=arg-1

'define emask=1'
'define emasklng=const(emask(e-' monm1 '),0,-u)'
'define emasksht=const(emask(e-' arg '),0,-u)'
'define emask=emasklng-emasksht'
'define emask=maskout(emask,emask-0.5)'
'define emaskinv=maskout(1,-1*const(emask,-1,-u))'
exit