| functional unit that generates its output variable as a function of its input variable according to a defined, time-invariant mathematical function|
|t||is the time;|
|u(t)||is the input variable;|
|f||is the function;|
|v(t)||is the output variable.|
Note 1 to entry: This entry was numbered 351-32-19 in IEC 60050-351:2006.