MAXEFFORT

Maximum amount of work to spend on the computation

Description

The environment variable MAXEFFORT determines the amount of effort allowed for heuristical parts of a computation, measured in "working units". The default value is MAXEFFORT = 1000000.

Possible values: Non-negative floating-point number; or infinity.

MAXEFFORT determines the maximum number of "working units" that may be spent on internal heuristics.

One working unit roughly corresponds to 1000 evaluation steps done by an average kernel function.

Whatever MAXEFFORT is set to, every MuPAD® function returns a correct though possibly unsimplified result; in particular, some functions may return unevaluated. MAXEFFORT determines the amount of additional time spent on obtaining a better or more simplified result; a value of infinity means that all built-in heuristics are really tried, a value of 0 means that all heuristics that might take considerable effort are left out.

A function whose result is uniquely specified has no way to react to MAXEFFORT.

Other functions carry out, in any event, all computations necessary to obtain some correct result; MAXEFFORT only determines the time available for improving that result. In case of functions that may return unevaluated immediately (e.g., solve or int), or may return their input immediately (as, e.g., simplify), or may answer a question by UNKNOWN immediately (as, e.g., is), all of their time consumption is counted to be spent on heuristics (purely heuristic functions).

Purely heuristic functions will usually return immediately if their input is quite complicated in relation to the effort allowed. This is also true if the user has provided that input on the interactive level. In order to pose a difficult problem where a longer running time is acceptable, MAXEFFORT should be increased.

A simplification achieved by heuristic methods may speed up the deterministic parts, such that a small value of MAXEFFORT does not necessarily decrease the total computing time.

The user may employ MAXEFFORT in his own functions as follows: any function may use the amount of effort given by MAXEFFORT partly for own overhead, and distribute the rest on the functions it calls. To do this, the caller has to save the variable MAXEFFORT and set it to whatever it wants to make available to the called function. Depending on whether the call is necessary to obtain a correct result at all and whether the called function is a heuristic one, there are the following cases to handle. If the call is necessary and the called function is deterministic, MAXEFFORT has no influence. If the call is not absolutely necessary and as far as the called function is deterministic, the caller has to subtract the necessary amount as own overhead from MAXEFFORT if enough is available; otherwise, such call must not take place. As far as the called function works heuristically (for whatever reason it was called), it has to limit its efforts to the amount given by MAXEFFORT.

In no event may the value of MAXEFFORT on entering a procedure be different from the value on leaving it, even not in case of an error. save must be used to ensure this.

No function may distribute and/or use more than the amount it has been given by its caller. The own overhead should be estimated; if it is supposedly small, MAXEFFORT may be ignored.

In order to avoid casual, not reproducible effects, e.g., by other programs running on the same computer, MAXEFFORT should not be used in connection with time measurement using time or rtime. For example, the running time saved in one recursive call according to time measurement must not be supplied to another recursive call.

Examples

Example 1

The decomposition of an integer into prime factors is unique; hence the result of ifactor is uniquely determined, such that ifactor does not react to MAXEFFORT:

MAXEFFORT:= 0:
ifactor(2^10 + 1)

Example 2

The function solve may return unevaluated. Hence it will do so if there is no effort left to spend on the computation:

MAXEFFORT:= 0: solve(ln(x) + x = 3, x)

See Also

MuPAD Functions

Was this topic helpful?