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FIT2D uses dynamic memory (or virtual memory) allocation to allow as much flexibility as possible in the size of data that can be treated. This has obvious advantages, but also has disadvantages. 2-D dimensional data (images) from modern detector systems can be very large, so the demands of FIT2D for memory allocation can be similarly large. Users are recommended to try to use the minimum of memory necessary for their data. At start-up the user is prompted for the initial size of program arrays i.e. the size necessary to input their data.
The user is also prompted as to whether or not error estimate arrays (variance arrays) are to be created. If created, the dynamic memory demands are roughly double and many operations will take longer as error propagation is being carried out. If error estimate arrays are not created, no error propagation is carried out, and any fitting will thus be unweighted.
If at any stage during the running of FIT2D the user gets a message that memory allocated has failed, it must be assumed that the previous command has failed. Recovery may be possible, but this depends on the circumstances.
(It is thought that Windows 95 limits the maximum memory size to
64 Mbytes. If this is the case it will be a severe limitation for
those wanting to work with large image sizes i.e. greater than 1024
1024. WindowsNT does not impose this limitation so may be
a solution for those wanting to use FIT2D from a Windows system.
Whether or not Windows 98 solves this problem is not presently known,
and FIT2D has yet to be tested on such a system.)
Andy Hammersley