"Geometry search array full" error message

In my FLUKA error file I find the message GEOMETRY SEARCH ARRAY FULL. What does this mean and can I ignore it?

This message indicates that insufficient memory has been allocated for the “contiguity list” (list of zones contiguous to each zone). This is not an actual error, but it is highly preferable that the user optimises the computing time by increasing the values of the NAZ variable in the geometry region specifications.

In particular, for each region, FLUKA sets up a list of “neighbour regions” to be tested first when a particle leaves any of the bodies making up that region.

If the new region is not found in the list, the other regions are searched. When found, the region is added to the list of neighbours, provided there is enough space left in the array. The space allocated is by default 5 neighbours per region, which is normally more than sufficient. The value can be modified by the user as explained in the manual (description of region data).

The integer in columns 6-10 is the number of regions which can be entered by a particle leaving any of the bodies defined for the region being described (leave blank in continuation cards). This number is used to allocate memory, and it is not essential that it is exact (if left blank in number-based geometry inputs, it is set to 5). Any number is accepted, and only the sum of all numbers indicated for each region matters. There is no need for this number to be close to the actual value for each individual region, provided the total is large enough. For example, setting NAZ to 91 for 1 region and to 1 for 9 other regions is exactly the same as setting it to 10 for all ten regions.

Note that memory allocation is done globally, not region by region. In general, the impact on the CPU time can vary wildly depending on whether the contiguity list is marginally small or severely underestimated, and on the overall complexity of the geometry. For complex geometries, with severely underestimated NAZ’s, the impact can be huge, while in other cases the impact might be marginal.