Difference between revisions of "Memoization"
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'''Memoization''' is a technique for storing values of a function instead of recomputing them each time the function is called. |
'''Memoization''' is a technique for storing values of a function instead of recomputing them each time the function is called. |
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| + | A classic example is the recursive computation of [[Fibonacci number]]s. |
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| + | The immediate implementation of Fibonacci numbers without memoization is horribly slow. |
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| + | Try <hask>slow_fib 30</hask>, not too much higher than that and it hangs. |
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| + | <haskell> |
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| + | slow_fib :: Integer -> Integer |
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| + | slow_fib 1 = 1 |
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| + | slow_fib 2 = 1 |
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| + | slow_fib n = slow_fib (n-2) + slow_fib (n-1) |
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| + | </haskell> |
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| + | The memoized version is much faster. |
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| + | Try <hask>memoized_fib 10000</hask>. |
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| + | <haskell> |
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| + | memoized_fib :: Integer -> Integer |
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| + | memoized_fib = |
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| + | let fib' 0 = 0 |
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| + | fib' 1 = 1 |
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| + | fib' n = memoized_fib (n-2) + memoized_fib (n-1) |
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| + | in (map fib' [0 ..] !!) |
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| + | </haskell> |
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== See also == |
== See also == |
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Revision as of 20:02, 5 August 2007
Memoization is a technique for storing values of a function instead of recomputing them each time the function is called.
A classic example is the recursive computation of Fibonacci numbers.
The immediate implementation of Fibonacci numbers without memoization is horribly slow.
Try slow_fib 30, not too much higher than that and it hangs.
slow_fib :: Integer -> Integer
slow_fib 1 = 1
slow_fib 2 = 1
slow_fib n = slow_fib (n-2) + slow_fib (n-1)
The memoized version is much faster.
Try memoized_fib 10000.
memoized_fib :: Integer -> Integer
memoized_fib =
let fib' 0 = 0
fib' 1 = 1
fib' n = memoized_fib (n-2) + memoized_fib (n-1)
in (map fib' [0 ..] !!)