How to speed up this DP?

Revision en8, by fakeac, 2018-09-10 14:48:23

I have the following recurrence:

Let's say that I have 1 array f and 1 function g. A function call to g takes O(1) time. Note that we do not want to edit the code of function g, its a scipy function. I just want to compute the values in the f array using the recurrence given below:

For simplicity, one can assume that the function g is similar to the binomial coefficient function. So, just for simplicity, assume that g(n, i) = number of ways of choosing i items from n items where n >= i. Is it possible to solve this assuming we can modify g and make some kind of recurrence?

f[n] = summation(f[n-i]*g(i, n)) for i in [1, 2, 3, 4, ..., n]

Base Case: f[0] = 1.

If we use the above recurrence, it will take O(n^2) time. Any way to reduce it to O(n*log(n)) ?

Thanks in advance.

Tags #dp, #recursion, dp optimasation

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  Rev. Lang. By When Δ Comment
en8 English fakeac 2018-09-10 14:48:23 4 Tiny change: 'se Case: f(0) = 1.\n\nI' -> 'se Case: f[0] = 1.\n\nI'
en7 English fakeac 2018-09-10 14:46:04 303
en6 English fakeac 2018-09-10 14:37:22 10 Tiny change: 'mation(f[n — i]*g(i, n)' -> 'mation(f[n-i]*g(i, n)'
en5 English fakeac 2018-09-10 14:36:42 79
en4 English fakeac 2018-09-10 14:33:32 10 Tiny change: ' 4, ..., n — 1]\n\nBase ' -> ' 4, ..., n]\n\nBase '
en3 English fakeac 2018-09-10 14:32:55 3 Tiny change: ': f(0) = 1\nIf we us' -> ': f(0) = 1.\n\nIf we us'
en2 English fakeac 2018-09-10 14:32:23 108
en1 English fakeac 2018-09-10 13:57:22 443 Initial revision (published)