SnnsRObject$setTTypeUnitsActFunc: Set the activation function for all units of a certain ttype.
Description
The function uses the function SnnsRObject$getAllUnitsTType to find all units of a certain
ttype, and sets the activation function of all these units to the given activation function.
Usage
# S4 method for SnnsR
setTTypeUnitsActFunc(ttype, act_func)