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
[EMAIL PROTECTED]
-Original Message-
From: Giovanni A. Cignoni [mailto:[EMAIL PROTECTED]
Sent: Tuesday, 19 June 2007 10:17 PM
To: simstds@larc.nasa.gov
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 :)
Ciao,
Giovanni.
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