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Language:
English
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Language:
English
21.6. Fibonacci Example: Calculate Rule
rule Calculate when // Bind f1 and s1 f1 : Fibonacci( s1 : sequence, value != -1 ) // Bind f2 and v2; refer to bound variable s1 f2 : Fibonacci( sequence == (s1 + 1), v2 : value != -1 ) // Bind f3 and s3; alternative reference of f2.sequence f3 : Fibonacci( s3 : sequence == (f2.sequence + 1 ), value == -1 ) then // Note the various referencing techniques. modify ( f3 ) { value = f1.value + v2 }; System.out.println( s3 + " == " + f3.value ); end
- When there are two
Fibonacci
objects with values not equal to -1, the Calculate rule is able to match them. - There are 50 Fibonacci objects in the Working Memory. A suitable triple should be selected to calculate each of value in turn.
- Using three Fibonacci patterns in a rule without field constraints to confine the possible cross products would result in many incorrect rule firings. The Calculate rule uses field constraints to correctly constraint the Fibonacci patterns in the correct order. This technique is called cross product matching.
- The first pattern finds any Fibonacci with a value != -1 and binds both the pattern and the field. The second Fibonacci does this too, but it adds an additional field constraint to ensure that its sequence is greater by one than the Fibonacci bound to
f1
. When this rule fires for the first time, the two constraints ensure thatf1
references sequence 1 andf2
references sequence 2. The final pattern finds the Fibonacci with a value equal to -1 and with a sequence one greater thanf2
. - There are three
Fibonacci
objects correctly selected from the available cross products. You can calculate the value for the thirdFibonacci
object that's bound tof3
. - The
modify
statement updates the value of theFibonacci
object bound tof3
. This means there is now another new Fibonacci object with a value not equal to -1, which allows the Calculate rule to rematch and calculate the next Fibonacci number. - Switching to the Audit view will show how the firing of the last Bootstrap modifies the
Fibonacci
object, enabling the "Calculate" rule to match. This then modifies another Fibonacci object allowing the Calculate rule to match again. This continues till the value is set for allFibonacci
objects.