Occam

Although Occam is very close to being the machine language of the INMOS Transputer, it has not been widely used except on machines based on transputers (e.g., Meiko CS-1, Parsytec, Telmat). In the 1980s, many transputer-based machines were purchased or built by research groups as a (then) very cost-effective source of computer cycles. 

Almost all groups that once developed code for occam have now switched to other languages. Moreover, occam never made the transition to other machines, and new versions of the Transputer have consistently lagged projected delivery dates. 

Linda ° is a memory model and a coordination language see Reference 9 for an introduction. Realizations of this model in C and FORTRAN are commercially available on many different platforms, including networks. The Linda memory is a tuple space, a tuple being an ordered collection of typed values. Tuples may be either passive or under evaluation (representing a thread of execution). 

C-Linda i provides six operations on tuples, out( ), in( ), rd( ), inp( ), rdp( ), and eval( ), which also coordinate access to tuples. For example, out( ) adds a tuple to tuple space in( ) blocks until it finds a tuple that matches the specified pattern, returns the requested data and removes the tuple from tuple space rd( ) performs the same operation as in() except the tuple is left in tuple space inp( ) and rdp( ) are nonblocking forms, which return true or false according to whether the request was satisfied eval() is similar to out() except that new processes are created to evaluate each field of a tuple. When all fields have been evaluated, the tuple becomes passive. 

The Linda model supports many different parallel programming paradigms. At its simplest, the distributed-data environment offers an improvement over raw message passing by promoting an uncoupled programming style. This is because the synchronization of processes resulting from access to distributed data is minimal. However, arbitrarily complex shared and distributed data structures may be created. 

The transputer s advantage in speed relative to common computer operations has also been boosted by reducing the number of basic instruction sets available to the programmer. This aspect is discussed next. 

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Microprocessors (transputers), with the help of a special language (Occam), can handle flows of information in a parallel fashion instead of sequentially (serially), thereby greatly increasing the speed of operation. Transputers also control the flow of information by communicating with each other. 

A special computer language (Occam) is needed to enable transputers to be programmed in this cooperative mode, yielding true parallel processing of information with all its advantages in speed. 

A postulated kinetic scheme is a model or hypothesis. In accord with Occam s razor, the model should be no more complex than is required to account for the... 

THERMOTECH Surrey Technology Centre 40 Occam Road The Surrey Research Park Guildford GU2 5YH Contact N. Saunders Tel +44 483 502003... 

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

A good model is consistent with physical phenomena (i.e., 01 has a physically plausible form) and reduces crresidual to experimental error using as few adjustable parameters as possible. There is a philosophical principle known as Occam s razor that is particularly appropriate to statistical data analysis when two theories can explain the data, the simpler theory is preferred. In complex reactions, particularly heterogeneous reactions, several models may fit the data equally well. As seen in Section 5.1 on the various forms of Arrhenius temperature dependence, it is usually impossible to distinguish between mechanisms based on goodness of fit. The choice of the simplest form of Arrhenius behavior (m = 0) is based on Occam s razor. 

Occam s Razor states that multiplicity ought not to be posited without necessity. This prin-... 

Mayer, I. Program Bondord, available at http //occam.chemres.hu... 

It cannot be emphasised too strongly that this entirely new hypothetical species lacks the essential feature of a scientific theory, namely that the newly invented species should have well-defined properties so that its existence can be tested by experiment moreover, it offends against Occam s Razor ( hypotheses must not be multiplied unnecessarily ). 

In the absence of any equations based on fundamental material behaviour, equations such as these should be used for extrapolation, although it is generally dangerous to extrapolate in this way by more that than one decade in time. Other empirical equations may be used, provided that Occam s principle is observed, i.e., the theory should be no more complicated than is necessary to fit the observations. Higher order polynomials in time should be avoided, since they have a tendency to diverge rapidly towards infinity, or minus infinity, when they are extrapolated beyond the range of measurements. 

It is advisable not to forget the parsimony principle, also called Occam razor, often paraphrased into... 

If unireactant enzyme behavior is not described adequately by existing equations, a reaction scheme should be constructed which seems to describe the behavior based on available experimental data. In doing so, Occam s razor should be applied and the simplest possible explanations should be first discounted before more complex explanations are proposed. 

For self-associating protein systems, third-order polynomial functions provided a good fit over the accessible range The data on AG° must show the direction of the chemical change, toward the minimum in the Gibbs function. If this proves true, the equation can be applied in the standard or nonstandard state. For protein unfolding or DNA unwinding, nonlinear models are needed Consistent with Occam s razor, the simplest description is used to describe the system, and complexity is increased only if warranted by the experimental results. 

OCCAM S RAZOR PRION PLAQUE FORMATION PROBABILITY STATISTICS (A Primer)... 

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