-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Lew Wolfgang wrote:
David C. Rankin wrote:
For an ill-defined requirement, an equally ill-defined guess at a solution. First, what information is held at each array address? My first thought was, "if nothing more than coordinates are held in the array, why store the information at all?" Sound loss through water seems like nothing more than a 3-dimensional space problem with decrease in signal amplitude resulting from propagation through a known medium being the answer. If that were the case, there would be no storage requirement at all. The response would be based on a pure computation of acoustic decay at or between points A and B with the source at point C.
Hi David,
Thanks for the reply, sorry I'm late in reply to yours! I've been really busy these days.
The data stored at each element describes the transmission loss between the two points. Sound propagation through a body of water is anything but uniform. Temperature differences give you density differences, also affected by salinity in ocean water, and you end up with a very complicated sound field. I'm fairly sure the data will be calculated in advance based on models.
Initially, this would rather suggest that you are dealing with the (graphical?) representation of the data rather than the calculation of the value of that data. In this case the issue with the array is moot, as the code really need only concern itself with translation of the data into the relevant visual format. You do not really need access to all of the data at any one time and the only thing that needs to be retained is the visual representation (which may be in the representational device). This explanation also suggests that some further processing is required, and therefore rather suggest the size of the array is the least of the issues involved. It looks as if the values for each cell need to be calculated not only from the status of the cell itself but from the status of adjoining cells. If the calculation involves iteration towards a stable solution then the there is an awful lot of brute force computation involved.
I think the researchers are already doing this, good observation!
From a code stand point, if you do need an array that large, then you will need whatever you write it in to access some type of "directory structure" to access the data with little or no computational overhead. A pure transactional database approach seems computationally expensive for accessing data that isn't changing. Hopefully FORTRAN has improved many times over in its data interfacing and has something more to offer than "common-block" access that was always a hindrance.
Some sideways thinking here may be appropriate. You seem to be talking about a number of cells which not only have values but relationships with other cells. With traditional arrays of values this might be rather difficult to handle as a representational structure. What you are really talking about is an array of cellular objects. Now I am not very sure that FORTRAN even in its modern form is really up to representing this effectively, C will if each object is a collection of values, C++ (if you are prepared for the culture shock) or some other compiled OOP language if each cell not has values but also functional relationships with other cells. All these languages are computationally effective, but C and C++ are more flexible about data representation and I/O than FORTRAN. (But this does not stop one using FORTRAN for the math and C/C++ for the data management and I/O). Even if you are only dealing with representation of data, an OOP related approach has potential advantages (if only for modelling the programming problem)..
Agree on the database overhead. There are apparently HPC projects that specialize in this kind of problem. I think they come as libraries that would be called by FORTRAN code. The HDF5 project is an example of this kind of library, but I have zero experience with them.
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