Log-space computable function

A log-space computable function is a function formula_1 that requires only formula_2 memory to be computed (this restriction does not apply to the size of the output). The computation is generally done by means of a log-space transducer.
Log-space reductions.
The main use for log-space computable functions is in log-space reductions. This is a means of transforming an instance of one problem into an instance of another problem, using only logarithmic space.