Avoid panel_decomposition_mod causing a divide-by-zero

[tom-j-h]

PR Summary

Sci/Tech Reviewer:
Code Reviewer:

This issue was found in development of the JADA benchmark.

Other changes made meant that jedi_lfric_tests was crashing due to a divide by zero here:

lfric_core/infrastructure/source/mesh/panel_decomposition_mod.f90

Line 252 in a4caea1

mp_num_cells_x = num_cells_x / mapping_factor

mp is initialised here:

lfric_core/infrastructure/source/mesh/panel_decomposition_mod.f90

Lines 879 to 885 in a4caea1

	! If no meshes were found, return 1. This is relevant for JEDI where mesh
	! initialisation is run twice.
	if ( shortest_panel_width < huge(0_i_def) ) then
	mp = this_panel_width / shortest_panel_width
	else
	mp = 1
	end if

The solution is to instead set mp = max(1, this_panel_width / shortest_panel_width).

Please note, I did not find this issue or develop the fix - I just need it for the linked PR below, and there wasn't a PR yet.

• linked Align jedi_lfric_tests linear model/adjoint testing to adjoint_tests and linear_model lfric_apps#156

• closes Avoid panel_decomposition_mod causing a divide-by-zero #226

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