The discrete option, as we originally intended it, was a nearest grid-point 
option. The relevant code snippet from the Janus interpreter:

     * allow for order 0 linear interpolation, i.e. take nearest discrete
     * value on the grid.
    if ( 0 == functionIndependentVariableOrder_[ index ][ i ] ) {
      if ( 0.5 >= frac[ i ] ) {
        frac[ i ] = 0.0;
      } else {
        frac[ i ] = 1.0;

We only use discrete where the inputs are meant to be one of the breakpoints. 
The "nearest" interpretation ensures we get the right answer if there is some 
issue with a data precision-related error (though we would normally use integer 
inputs anyway). However, I can also see the utility of a "threshhold" approach 
as you have described (eg, ISA properties as a function of pressure altitude). 
You could always shift the breakpoints to achieve the same thing, or use 
MathML. I agree it needs to be clearly documented.

Regards, Rob

Rob Curtin
Ball Solutions Group
on contract to Air Vehicles Division,
Defence Science & Technology Organisation
Tel: +61 (0)3 9626 7730
Fax: +61 (0)3 9626 7705

-----Original Message-----
From: Giovanni A. Cignoni [mailto:[EMAIL PROTECTED] 
Sent: Tuesday, 19 June 2007 10:17 PM
Subject: Re: Re: Discrete interpolation attribute (was New version of DAVEfunc 
DTD 1.9b3)

> so the independent values state where the function changes value.
> Nearest-neighbor would put the transitions exactly between the 
> independent break points.

So at the end is just truncation vs approximation, but being in sync with names 
is anyway important :)


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