prefix-sum | 易学教程

Gathering results of MPI_SCAN

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问题 I have this array [1 2 3 4 5 6 7 8 9] and i am performing scan operation on that. I have 3 mpi tasks and each task gets 3 elements then each task calculates its scan and returns result to master task task 0 - [1 2 3] => [1 3 6] task 1 - [4 5 6 ] => [4 9 15] task 2 - [7 8 9] => [7 15 24] Now task 0 gets all the results [1 3 6] [4 9 15] [7 15 24] How can I combine these results to produce final scan output? final scan output of array would be [1 3 6 10 15 21 28 36 45] can anyone help me please?

Dynamic prefix sum

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问题 Is there any data structure which is able to return the prefix sum [1] of array, update an element, and insert/remove elements to the array, all in O(log n)? [1] "prefix sum" is the sum of all elements from the first one up to given index For example, given the array of non-negative integers 8 1 10 7 the prefix sum for first three elements is 19 ( 8 + 1 + 10 ). Updating the first element to 7 , inserting 3 as the second element and removing the third one gives 7 3 10 7 . Again, the prefix sum

opencl- parallel reduction without local memory

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问题 Most of the algorithms for parallel reduction uses shared(local) memory. Nvidia,AMD, Intel and so on. But if devices has doesn't have shared(local) memory. How can I do it? If i use same algorithms but store temporary value on global memory, is it gonna be work fine? 回答1: If I think about it, my comment already was the complete answer. Yes, you can use global memory as a replacement for local memory but: you have to allocate enough global memory for all workgroups and assign the workgroups

CONFLICT_FREE_OFFSET macro used in the parallel prefix algorithm from GPU Gems 3

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问题 First of all, here is the link to the algorithm: GPU Gems 3, Chapter 39: Parallel Prefix Sum (Scan) with CUDA. In order to avoid bank conflicts, padding is added to the shared memory array every NUM_BANKS (i.e., 32 for devices of computability 2.x) elements. This is done by (as in Figure 39-5): int ai = offset*(2*thid+1)-1 int bi = offset*(2*thid+2)-1 ai += ai/NUM_BANKS bi += ai/NUM_BANKS temp[bi] += temp[ai] I don't understand how ai/NUM_BANKS is equivalent to the macro: #define NUM_BANKS 16

Dynamic prefix sum

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Is there any data structure which is able to return the prefix sum [1] of array, update an element, and insert/remove elements to the array, all in O(log n)? [1] "prefix sum" is the sum of all elements from the first one up to given index For example, given the array of non-negative integers 8 1 10 7 the prefix sum for first three elements is 19 ( 8 + 1 + 10 ). Updating the first element to 7 , inserting 3 as the second element and removing the third one gives 7 3 10 7 . Again, the prefix sum of first three elements would be 20 . For prefix sum and update, there is Fenwick tree . But I don't