Editing Trial and error (section)

===Simplest applications===
[[William Ross Ashby|Ashby]] (1960, section 11/5) offers three simple strategies for dealing with the same basic exercise-problem, which have very different efficiencies.  Suppose a collection of 1000 on/off switches have to be set to a particular combination by random-based testing, where each test is expected to take one second. [This is also discussed in Traill (1978–2006, section C1.2]. The strategies are:
*the perfectionist all-or-nothing method, with no attempt at holding partial successes. This would be expected to take more than 10^301 seconds, [i.e., 2^1000 seconds, or 3·5×(10^291) centuries]
*a serial-test of switches, holding on to the partial successes (assuming that these are manifest), which would take 500 seconds on average
* parallel-but-individual testing of all switches simultaneously, which would take only one second

Note the tacit assumption here that no intelligence or insight is brought to bear on the problem. However, the existence of different available strategies allows us to consider a separate ("superior") domain of processing — a ''"meta-level"'' above the mechanics of switch handling — where the various available strategies can be randomly chosen. Once again this is "trial and error", but of a different type.