Editing Input syntax manual (section)

=== set nfg ===

 '''set nfg''' ''ERG''

Defines the few-group structure used for group constant generation. Input values

{|
| <tt>''ERG''</tt>
| : Name of the few-group structure used for group constant generation (default value: [[Pre-defined energy group structures#Default 2-group structure|Default 2-group structure]], 2 energy-groups)
|}

 '''set nfg''' ''NE''

Defines the few-group structure used for group constant generation. (This syntax should not be used anymore). Input values:

{|
| <tt>''NE''</tt>
| : Number of energy groups (1/2/4) corresponding to Serpent 1 default 1-, 2- or 4-group structure.
|}

 '''set nfg''' ''NE E<sub>NE-1</sub> E<sub>NE-2</sub> ... E<sub>1</sub>''

Defines the few-group structure used for group constant generation. (This syntax should not be used anymore). Input values:

{|
| <tt>''NE''</tt>
| : Number of energy groups. Must be at least 2 in this format.
|-
| <tt>''E<sub>N</sub>''</tt>
| : Energy group boundary value between groups ''N'' and ''N+1'' [in MeV]. Values have to be given in ascending order.
|}

<u>Notes:</u>

*The few-group structure may be an energy grid defined using the [[#ene|ene card]] or a name of a [[pre-defined energy group structures|pre-defined energy group structure]].
*The few-group structure must be a sub-set of the intermediate multi-group structure.
*The default is a two-group structure with boundary between fast and thermal group set to 0.625 eV (see [[Pre-defined energy group structures#Default 2-group structure|Default 2-group structure]])).
**Serpent uses an intermediate multi-group structure in the calculation. The default structure consists of 70 groups (see [[Pre-defined energy group structures#Default multi-group structure|Default multi-group structure]]), and can be changed using the [[#set micro|set micro]] or [[#set fum|set fum]] options.
**In general, the intermediate multi-group structure should have more groups than the few-group structure to get reasonable results for [[#set fum|leakage corrected group constants]] and out-scatter diffusion coefficients.
*See also: [[Output parameters#Homogenized group constants|homogenized group constants output]].
*The few-group structure will also be used for example for [[#set adf|assembly discontinuity factors]] and [[#set alb|albedos]].