Re: [Jsbsim-devel] Multi-dimensional tables

[Dennis J. L. <js...@li...>]

Jon,

1) Good stuff!

2) OK, gridded, not sparse.  How about orthogonal?  From the example you
provided, (repeated below), does the mach independent variable need to
have the same breakpoints?  From the appearance, below, it would appear
that the answer is "no", which is good, as it is more flexible (at the
expense of storage space and possibly some computation speed-up tricks).

And if "no", then it can be used to sort address Alan's point, whether
you intended to or not.

<function name="bigWhatever1">
  <interpolate1d>
    <p> aero/qbar-psf </p>
    <v> 0 </v>  <interpolate1d>
                  <p> velocities/mach </p>
                  <v> 0.00 </v>  <table> ... table 1 definition ...
                  <v> 0.80 </v>  <table> ... table 2 definition ...
                  <v> 0.90 </v>  <table> ... table 3 definition ...
                 </interpolate1d>
    <v> 65 </v> <interpolate1d>
                  <p> velocities/mach </p>
                  <v> 0.00 </v>  <table> ... table 1 definition ...
                  <v> 0.80 </v>  <table> ... table 2 definition ...
                  <v> 0.90 </v>  <table> ... table 3 definition ...
                </interpolate1d>
    <v> 90 </v> <interpolate1d>
                  <p> velocities/mach </p>
                  <v> 0.00 </v>  <table> ... table 1 definition ...
                  <v> 0.80 </v>  <table> ... table 2 definition ...
                  <v> 0.90 </v>  <table> ... table 3 definition ...
                </interpolate1d>
  </interpolate1d>
</function>


3) And as one who has implemented such things as well, about about
monotonicity of independent variables.  Is that checked/enforced?  That
can be bear of a typo to debug, and can cause algorithms to get really
confused.

Dennis


On 2013-06-10 9:01 AM, Jon S. Berndt wrote:
> 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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