Re: [Jsbsim-devel] Multi-dimensional tables

[Jon S. B. <jon...@co...>]

Dennis - I hadn't thought of that, but, yes, that will work. Each individual
table does not have to have the same set of breakpoints.

Jon


> -----Original Message-----
> From: Dennis J. Linse [mailto:js...@li...]
> Sent: Monday, June 10, 2013 9:48 AM
> To: Development issues
> Subject: Re: [Jsbsim-devel] Multi-dimensional tables
> 
> So, Jon, (without looking at the code) will this work for Alan?
> 
> <function name="bigWhatever1">
>   <interpolate1d>
>     <p> velocities/mach </p>
>     <v> 0.1 </v>  <interpolate1d>
>                   <p> ???/alpha </p>
>                   <v> -10.0 </v>  <v> ?? </v>
>                   <v>   0.0 </v>  <v> ?? </v>
>                   <v>  30.0 </v>  <v> ?? </v>
>                  </interpolate1d>
>     <v> 0.9 </v> <interpolate1d>
>                   <p> ???/alpha </p>
>                   <v> -2.0 </v>  <v> ?? </v>
>                   <v>  0.0 </v>  <v> ?? </v>
>                   <v>  5.0 </v>  <v> ?? </v>
>                 </interpolate1d>
>     <v> 2.0 </v> <interpolate1d>
>                   <p> ???/alpha </p>
>                   <v> -1.0 </v>  <v> ?? </v>
>                   <v>  0.0 </v>  <v> ?? </v>
>                   <v>  1.0 </v>  <v> ?? </v>
>                 </interpolate1d>
>   </interpolate1d>
> </function>
> 
> I'm guessing yes, by the way that you describe the tables since the
> dependent value can be a table/function, etc.  So each dimension needs
> to be calculated separately at two different breakpoints and then
> interpolated.  (The traditional, orthogonal, multi-dimensional matrix
> approach has only a single set of breakpoints in each dimension then
> uses integer indices to get into the table, therefore, it has to be
> "full".)   If it is just linear in each dimension, it should work,
> right?
> 
> Dennis
> 
> On 2013-06-10 10:23 AM, Alan Teeder wrote:
> >
> > Yes Sean got the words that I meant. ;-) Thanks.
> >
> > What I am looking for is a way to break up the coefficient tables
> into
> > sections that are split into the high alpha ranges that are
> applicable
> > at low speeds, and low alpha ranges which are achievable at high
> speeds.
> >
> > My WIP stalls at 30 degrees incidence on the approach, but would
> > probably break the airframe at 5 degrees when supersonic.
> >
> > At the moment each coefficient has a table covering the whole
> > incidence range for each Mach number, so in this case the tables
> cover
> > the range -10 to 40 degrees incidence and Mach numbers 0-2. .
> >
> > My solution at the moment is to extrapolate the data to make up
> > numbers to fill in the grid at the high speed end, but these numbers
> > are really just meaningless rubbish and are only there to complete a
> sparse matrix.
> >
> > -----Original Message-----
> > From: Jon S. Berndt
> > Sent: Monday, June 10, 2013 3:01 PM
> > To: 'Development issues'
> > Subject: Re: [Jsbsim-devel] Multi-dimensional tables
> >
> > Ah, yes - thanks for that. That explains it. JSBSim table lookups
> only
> > do gridded tables - not ungridded/sparse. There are a number of
> > methods one could take to fill in the blanks and IMHO it's better to
> do that offline.
> > It's sort of an art, in my experience.
> >
> > Jon
> >
> >> -----Original Message-----
> >> From: Sean McLeod [mailto:se...@se...]
> >> Sent: Monday, June 10, 2013 6:50 AM
> >> To: Development issues
> >> Subject: Re: [Jsbsim-devel] Multi-dimensional tables
> >>
> >> I think what Alan is asking/looking for is whether there is any
> >> sparse data table support.
> >>
> >> So for example if he has data for some coefficient that is dependent
> >> on
> >> 2 dimensions, say mach  number and AoA but for low mach numbers he
> >> has data for a range of AoAs from say -5 to +20 but for higher mach
> >> numbers he only has data for an AoA range from -3 to +5.
> >>
> >> He doesn't want to be forced to make up data for the higher mach
> >> numbers for AoA ranges from -5 to -3 and from +5 to +20 to match the
> >> AoA range of the data he has for lower mach numbers.
> >>
> >> Cheers
> 
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