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.
IMPORTANT: This email remains the property of the Australian Defence
Organisation and is subject to the jurisdiction of section 70 of the CRIMES ACT
1914. If you have received this email in error, you are requested to contact
the sender and delete the email.
