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.