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As of version 1.9.0-beta9 ProB allows you to annotate functions in the ABSTRACT_CONSTANTS section for memoization. | As of version 1.9.0-beta9 ProB allows you to annotate functions in the ABSTRACT_CONSTANTS section for memoization. | ||
[https://en.wikipedia.org/wiki/Memoization Memoization] is a technique for storing results of function applications and reusing the result if possible to avoid re-computing the function for the same arguments again. | |||
To enable memoization you either need to | To enable memoization you either need to | ||
* annotate the function in the ABSTRACT_CONSTANTS section with the pragma <tt>/*@desc memo */</tt> | |||
* set the preference <tt>MEMOIZE_FUNCTIONS</tt> to true. In this case ProB will try to memoize all functions in the ABSTRACT_CONSTANTS section, unless they are obviously small and finite and can thus be precomputed completely. | |||
Take the following example: | Take the following example: | ||
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fib(30)=1346269; | fib(30)=1346269; | ||
END | END | ||
Memoization means that the recursive Fibonacci function now runs in linear time rather than in exponential time. | |||
Generally, memoization is useful for functions which are complex to compute but which are called repeatedly with the same arguments. | |||
= Memoization of Function Calls =
As of version 1.9.0-beta9 ProB allows you to annotate functions in the ABSTRACT_CONSTANTS section for memoization. Memoization is a technique for storing results of function applications and reusing the result if possible to avoid re-computing the function for the same arguments again.
To enable memoization you either need to
Take the following example:
MACHINE MemoizationTests
ABSTRACT_CONSTANTS
fib /*@desc memo */,
fact /*@desc memo */
PROPERTIES
fib = %x.(x:NATURAL |
(IF x=0 or x=1 THEN 1
ELSE fib(x-1)+fib(x-2)
END))
&
fact = %x.(x:NATURAL|(IF x=0 THEN 1 ELSE x*fact(x-1) END))
ASSERTIONS
fib(30)=1346269;
END
Memoization means that the recursive Fibonacci function now runs in linear time rather than in exponential time. Generally, memoization is useful for functions which are complex to compute but which are called repeatedly with the same arguments.