Last version:
FLUKA 2021.2.8, November 20th 2022
(last respin 2021.2.8)
flair-2.3-0c 11-Sep-2022


-- Fluka Release
( 20.11.2022 )

FLUKA 2021.2.8 has been released.

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Output and Error messages


If I change the value of a magnetic field in my problem, the program suddenly starts to output error messages of the type:
 MAGNEW,TXYZ:  0.31640638004497
 U,V,W -6.56290015166051E-04  9.07632797085983E-03  0.56242650150838


In option MGNFIELD, one inputs the components of the magnetic field, but if they are set all = 0, a user subroutine MAGFLD is called, with the following arguments: ( X, Y, Z, BTX, BTY, BTZ, B, NREG, IDISC ). Here, BTX, BTY and BTZ ARE NOT the components, but the direction cosines! The absolute value is given by B. Looking at the direction cosines printed in the error message, it is clear that U, V and W (the direction cosines) are not properly normalised. The sum of their squares is 0.316406, as shown by the TXYZ value).


I get the following message: **** Photonuclear interaction not performed because of missing room in FLUKA stack *** What shall I do?


Probably you did excessive biasing of the interaction length (WHAT(2) of option LAM-BIAS), and you got too many interactions. Try increasing the absolute value of WHAT(2): the smaller the reduction factor, the stronger the biasing.


I get in my FLUKA error file 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 optimise computer 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 be 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 it can be hard to appreciate.


In the output file, what does the "missing energy" value indicate?


Don't worry: the "missing energy" means nothing wrong, it is a honest physical quantity! It is what we call "Q" in nuclear physics. When you have an endoenergetic nuclear reaction, for instance a (n,2n) reaction, you have a positive missing energy (Q<0). It is missing because which it has been transformed into mass of the final nucleus. When you have an exoenergetic nuclear reaction, for instance a (n,gamma) or a thermal fission, you have a negative "missing energy" (Q>0). That means, energy is not missing at all, but is created out of nuclear binding energy balance. In the end, FLUKA does its total energy balance, which can be positive or negative. In a pure electromagnetic run, the missing energy is practically zero. In a run with nuclear reactions, it can be positive or negative. With a thermal neutron source or with fissionable materials the missing energy can usually have a very large negative value. With Pb and Ta, as in your case, a lot of energy is needed to break the nucleus (think of all reactions having an energy threshold), and the missing energy can be positive. The value you found of 6.3% is not particularly high.


The error file contains the following message. What does this mean and can I ignore it?
  Geofar: Particle in region 3 (cell # 0) in position 1.000000000E+00
  0.000000000E+00 1.000000000E+00
   is now causing trouble, requesting a step of 6.258867675E-07 cm
   to direction -2.285059979E-01 -9.412338141E-01 2.487245789E-01, error count: 0
   Particle index 3 total energy 5.189748600E-04 GeV Nsurf 0
  We succeeded in saving the particle: current region is n. 2 (cell # 0)


The message indicates a real problem if repeated more than a few times. As it can be seen, the program has some difficulty to track a particle in a certain direction, and it tries to fix the problem by "nudging" the particle by a small amount, in case the problem is due to a rounding error near a boundary. If the message appears often, it is recommended to run the geometry debugger centering around the position reported in order to find if there is an error in the geometry description.

Last updated: 26th of April, 2016

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