Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.


Paul
Posts:
426
Registered:
2/23/10


Re: Efficient general purpose 1D lookup table?
Posted:
Dec 11, 2013 11:51 AM


On Sunday, December 8, 2013 9:05:23 PM UTC5, Steven Lord wrote: ><paul.domaskis_AT_gmail.com> wrote: >> I was in fact using a similar approach as your nonsparse lookup >> table. Since the allowable input values are not continguous, it >> would be nice if the input argument didn't have to be continuous >> (matrix indexes have to be). > > I'm not sure what you mean here. In a sparse matrix, only the > nonzero elements are stored. If you have a nonzero element in row 1 > and a nonzero element in row 1000000, that sparse matrix stores just > those two nonzero values.
Yes, but you still get a valid return value (zero) when the index points to a zero value. I don't want to have to trap zeros because zero is one of the valid values to be returned in a lookup.
>> ...And it would be >> good if I could cause some kind of abnormality like use NaNs in >> place of the zeros in a sparse matrix. > > The FULL command is just to display the results nicely. It's not > necessary if you want to work with the values. > > sparseFoundValues = lookupTable(valuesToFind, 1); for k = > 1:length(interpolationLocations) % Do something with > interpolationLocations(k) and sparseFoundValues(k) end % or just > work with the whole vectors > plot(interpolationLocations,sparseFoundValues)
Understood, thanks. However, it seems to me that I would have to work with full matrix just to stick NaNs into locations where the input argument should be invalid. If I understood correctly.
>> Currently, I avoid the issue by restricting myself to contigous >> input values starting from 1. Strictly speaking, I could encounter >> situations where that isn't the case, so I was hoping to write code >> that handles those situations without adding to much to the code >> (and ideally without departing from vectorization).



