ATC: fix_modify AtC initial

# fix_modify AtC initial

## syntax

fix_modify AtC initial <field> <nodeset> <constant | function>

- <field> = field name valid for type of physics, temperature | electron_temperature
- <nodeset> = name of set of nodes to apply initial condition
- <constant | function> = value or name of function followed by its parameters

## examples

`fix_modify atc initial temperature groupNAME 10.`

## description

Sets the initial values for the specified field at the specified nodes.

## restrictions

keyword 'all' reserved in nodeset name

## default

none