Default importances are not printed in newly created cells

[tjlaboss]

Bug Description

Cells in MCNP have an importance parameter. This is set using montepy.data_inputs.importance.Importance objects. When a file is written out, importances are either required or highly recommended for all cells, depending on the situation.

In MontePy, a cell's importance may be set by using Importance.all or Importance.particle for a particular particle type (neutron, electron, etc.). However, when setting the importance of a newly created cell, the importance is not always printed:

• When not setting an importance value, accepting the default value
• When setting cell.importance.all to any value
• When explicitly setting all importances to the default value individually

It does work:

• When setting an importance individually to a non-default value
• When explicitly setting an importance to the default value when also setting another importance on the same cell to a non-default value

I suspect this has something to do with detecting whether the parameter has changed, attempting to preserve original user formatting.

To Reproduce

See below. Cells are added to a problem with mode n p in a variety of ways.

import io
import montepy

deck = montepy.read_input("base_problem.i")

# Modify an existing cell. Importance remains.
deck.cells[1].geometry &= +deck.surfaces[2]
# Cell 2 should give "imp:n=2.0 imp:p=2.0"
c2 = montepy.Cell(number=2)
c2.geometry = -deck.surfaces[2] & +deck.surfaces[3]
c2.importance.all = 2.0
deck.cells.append(c2)
# Cell 3 should give "imp:n=1.0 imp:p=1.0"
c3 = montepy.Cell(number=3)
c3.geometry = -deck.surfaces[3] & +deck.surfaces[4]
c3.importance.neutron = 1.0
c3.importance.photon = 1.0
deck.cells.append(c3)
# Cell 4 should give "imp:n=4.0 imp:p=1.0"
c4 = montepy.Cell(number=4)
c4.geometry = -deck.surfaces[4]
c4.importance.neutron = 4.0
deck.cells.append(c4)
# Cell 5 DOES give "imp:n=5.0 imp:p=1.0"
c5 = montepy.Cell(number=5)
c5.geometry = -deck.surfaces[5]
c5.importance.neutron = 5.0
c5.importance.photon = 1.0
deck.cells.append(c5)
# Ensure that this is set:
# Ensure that this is set:
deck.print_in_data_block["imp"] = False

stream = io.StringIO()
deck.write_problem(stream)
stream.seek(0)
print(stream.read())
stream.close()

Input MCNP file snippet

Details

base_problem.i

Example MCNP Input File
C cells
1 1 20 -1
        imp:n,p=1 
9 0     +1  imp:n,p=0
C New cells are added here without importance parameters

C surfaces
1 SO 9
2 SO 8
3 SO 7
4 SO 6
5 SO 5

C data
mode n p
C materials
C UO2 5 atpt enriched
m1       92238.80c  1.0
c transforms
c run parameters
ksrc  0.0  0.0  1.0
kcode 100 0.1 1 11

Output MCNP file snippet

Details

Example MCNP Input File
C cells
1 1 20 -1
         2 imp:n,p=1 
9 0     +1  imp:n,p=0
C New cells are added here without importance parameters
2 0 -2 3 
3 0 -3 4 
4 0 -4 IMP:n=4.0 
5 0 -5 IMP:n=5.0 IMP:p=1.0 

C surfaces
1 SO 9
2 SO 8
3 SO 7
4 SO 6
5 SO 5

C data
mode n p
C materials
C UO2 5 atpt enriched
m1       92238.80c  1.0
c transforms
c run parameters
ksrc  0.0  0.0  1.0
kcode 100 0.1 1 11

Version

• Version 1.2

Additional context

Related: #657, #735

[MicahGale]

I think this is less a bug and more a question of what should the default behavior be: implicit or explicit?

[tjlaboss]

Explicit is better than implicit; however, the default importance is 1.0 since #735 (before which it was 0.0). The documentation for Cell.importance declares a default of 1.0 (i.e., implicit). I think this is a bug.

If requiring explicitly setting importance is intentional, then the behavior for Cell 4 would not be a bug. In either case, the behavior for Cell 2 and Cell 3 in the example are bugs, because they explicitly set importance and do not print it.

[MicahGale]

Yeah touche. Maybe we need to go back to having a "flag" for when users manually set values and override default behavior with that.