Stochastic calculator

The concept of calculator stochastic is already old (for the young history of data processing) and contemporary of research and applications developed at the any end of the decade 1950 and until the middle of the decade 1970.

Their definition in the GDEL [Grand Dictionnaire Encyclopédique Larousse] is: "Calculator in which information is coded by a probability".

The problem

Numerical calculation

Until worms the middle of the years 1970, the computers were expensive and there was no question of associating some with each industrial process which one was to supervise or order. It was thus necessary to resort to:

* maybe with techniques of real-time allowing the division of the machines - slow at the time - with the help of delicate and expensive programming (real-time should not be confused with the time-sharing, where each process is made allocate a section of time in turn),
* maybe with industrial automats of price less raised, but flexibility lack: few or not possible calculation, orders mainly by "all or nothing" in line entry.

Analogue computation

Another approach, that of the analogue computers, had two disadvantages: the cost of realization of the circuits of multiplication and their slowness. The technique of hybrid calculation consisting in associating an analogue computer with a digital computer was not real success.

Industrial automats

The industrial automats made up of a simple memory (see article) offered a tempting solution, but limited to controls or operations of the type “all or nothing”, therefore flexibility lack for the regulation of processes requiring a monitoring and/or an order fines.

A new way

With beginning of the year 1960 of the researchers of the Alsthom company had the idea to represent a size between 0 and 1 by a probability of presence of one 1 on a line. A multiplication then required nothing any more but one simple and logical (very cheap circuit to produce) at a very good speed: the estimate with 1% of the probability required only 10ms with a frequency of 10,000 Hz. Still it for that was necessary that the entries are décorrélées, which was carried out by a small auxiliary attachment containing a generator random and of an exclusive-OR gate (XOR).

Technical stochastic calculation

The stochastic addition was a little more complex, because a probability remains by definition ranging between 0 and 1 both included. A system with three logical doors allowed starting from p1 and p2 on two entries to obtain at exit (p1+p2) /2. It was thus allocated to the user to remember that the value was on this line on scale 1/2, and to carry out the recalibration of its results at exit.

tarting and decline

The calculators stochastic, cheap, reliable and easy to produce in great quantity, were regarded in the years 1970 as promising substitutes with the fluidic circuits used in the military and industrial world. However the production at increasingly weak prices of microprocessors made lose interest with these systems. Their theory keeps nevertheless a ludic attraction today, and it is possible to manufacture with few expenses (or to emulate on computer) stochastic calculators. Their excellent reliability and their fast reaction time could make them again useful a day in the industrial processes or the military applications - if it is not already done.

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