I also agree that this is a good question. There are times when interrogating data where it is necessary to return either a truncated value, as you describe Bruce, or the nearest neighbour. Thus a single 'discrete' attribute may not have been the best suggestion. This is something we had overlooked in suggesting such an attribute. At the risk of fattening the dtd with unnecessary options, having attributes for both these cases would be useful.

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At present, the data tables I am currently using the 'discrete' attribute for are more akin to nearest-neighbour. Regards Geoff -----Original Message----- From: Bruce Jackson [mailto:[EMAIL PROTECTED] Sent: Tuesday, 19 June 2007 3:40 AM To: Giovanni A. Cignoni Cc: simstds@larc.nasa.gov Subject: Re: Discrete interpolation attribute (was New version of DAVEfunc DTD 1.9b3) On Jun 18, 2007, at 1:28 PM, Giovanni A. Cignoni wrote: >> The main change to the DTD is addition of 'discrete' as a supported >> interpolation method for tabular data, yielding a stair- step >> response from such a function. This came from a suggestion from >> Geoff Brian of Australia's DSTO. > > "Discrete" interpolation is the method also known as "nearest > neighbor"? > Being x in [a, b], f(x) is f(a) or f(b) depending on x being nearer to > a or b. Correct? > > Thanks in advance, ciao, > Giovanni Cignoni. > This is a good question, Giovanni. I see that we need to be much more rigorous in our definition of 'discrete' as it applies to these tables. I had assumed the interpretation would be as follows (I don't think this is 'nearest-neighbor')... In the case of a one-dimensional function, if the independentVarPts are defined as [a, b, c, d] and an arbitrary griddedTable points are defined as [8.5, 9.0, 9.5, 10.0] the function f(x) would be evaluated as shown below: f(x) ^ | 10.0 - | o | | | | 9.5 - | o------o | | | | 9.0 - | o------o | | | | 8.5 - | o------o | |----------------------------------> X | | | | a b c d so the independent values state where the function changes value. Nearest-neighbor would put the transitions exactly between the independent break points. I'd appreciate any feedback on this topic, especially from Geoff Brian who is apparently making use of this 'extension' to DAVE-ML. -- Bruce 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.