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我有算法为输入元素的每个组合执行计算,例如对于 100 个元素集中的每个 5 个元素子集。我正在将它移植到 GPU,现在我已经准备好了它的初始版本。为了加快速度,我想从本地内存加载数据,这是有限的(例如 32KB)并且可以容纳 100 个中的 20 个输入元素。所以我必须以某种方式划分我的工作并生成块组合。现在这是困难的部分,如何做到这一点。很可能我必须首先加载 20 个元素的数据,然后对这 20 个元素的 5 个元素子集进行计算。在此之后,我将不得不用新的替换它们中的一些(或全部)并为它们执行计算,然后冲洗并重复。你能告诉我我应该如何在本地内存中选择替换元素,以避免重复工作吗?到目前为止,我得出的结论是,我必须一次更换至少 16 个,以避免重复工作问题。
编辑:这是从 5 个元素中生成 2 个元素组合的示例。以下是所有可能情况的完整列表:
1, 2
1, 3
1, 4
1, 5
2, 3
2, 4
2, 5
3, 4
3, 5
4, 5
1, 2
1, 3
2, 3
1, 4
1, 5
4, 5
1, 2 // duplicate
1, 4 // ok, new
2, 4 // ok, new
2, 4
2, 5
3, 4
3, 5
最佳答案
说例如你有 100 个元素,你可以在内存中保存 20 个,你需要所有 5 个元素的组合,其中有 C(100,5) = 75,287,520。
为了能够生成所有组合,每个 5 个元素的组合都必须在某个时间点在内存中。这可以通过将元素分成 20/5 = 4 个元素的组来完成;输入中有 25 个这样的组,C(25,5) = 53,130 个组的组合。
对于每个组的组合,我们将首先从五个组中的每一个中生成一个元素的组合;这给了我们 53,130 x 45 = 54,405,120 个独特的组合。
我们现在有了每个元素来自不同组的组合,即分区 [1,1,1,1,1]。我们仍然需要找到分区 [2,1,1,1]、[2,2,1]、[3,1,1]、[3,2] 和 [4,1] 的组合。最简单的方法是在单独的阶段执行此操作,但最快的方法当然是将这些合并到 [1,1,1,1,1] 的第一阶段,因为我们将永远需要在第一阶段的某个时刻加载到内存中。
对于分区 [2,1,1,1],我们将依次加载每个组作为具有 2 个元素的组,然后从其余 24 个组中加载 3 个组的每个组合,并从每个组中取出一个元素。这将需要 25 x C(24,3) = 50,600 个步骤,每个步骤产生 C(4,2) x 43 = 384 个组合,或总共 19,430,400 个。
像 [2,2,1] 这样的分区有点不同,因为我们将依次加载每个组作为具有 2 个元素的第一组,但只有在它之后的组作为具有 2 个元素的第二组,以便避免重复。然后对于其中的每一个,我们将加载其他 23 个组中的每一个以获得最终元素。这将需要 C(25,2)/2 x 23 = 6,900 个步骤,每个步骤产生 C(4,2) x C(4,2) x C(4,1) = 144 个组合,总共 993,600 个。
分区 [3,1,1] 需要 25 x C(24,2) = 25 x 276 = 6,900 个步骤,每个步骤产生 C(4,3) x 42 = 64 个组合,总共 441,600 个。
分区 [3,2] 需要 25 x 24 = 600 个步骤,每个步骤产生 C(4,3) x C(4,2) = 24 个组合,总共 14,400 个。
分区 [4,1] 需要 25 x 24 = 600 个步骤,每个步骤产生 C(4,4) x C(4,1) = 4 个组合,总共 2,400 个。
所以我们总共有:
[1,1,1,1,1] -> 54,405,120
[2,1,1,1] -> 19,430,400
[2,2,1] -> 993,600
[3,1,1] -> 441,600
[3,2] -> 14,400
[4,1] -> 2,400
----------
75,287,520 combinations
正如您会注意到的,分区 [3,2] 和 [4,1] 都需要两组的每种组合,因此它们可以轻松集成到一个阶段。当然,如果将它们全部集成到 [1,1,1,1,1] 的第一阶段,则只需将 53,130 个组组合加载到内存中,这是绝对最小值。
A B C D E
1 2 3 4 5 <- ABCDE
1 2 3 4 6 <- ABCDE
...
1 2 3 4 25 <- ABCDE
1 2 3 5 6 <- ABCDE
...
1 2 3 24 25 <- ABCDE
1 2 4 5 6 <- ABCDE
...
1 2 23 24 25 <- ABCDE
1 3 4 5 6 <- ABCDE
...
1 22 23 24 25 <- ABCDE
2 3 4 5 6 <- ABCDE
...
21 22 23 24 25 <- ABCDE
可以通过取[2,1,1,1]、[1,2,1,1]、[1,1,2,1]和[1,1,1,2]元素来整合四部分的分区来自四组的这些组合:
A B C D E
1 2 3 4 5 <- ABCD ABCE ABDE ACDE BCDE
1 2 3 4 6 <- ABCE ABDE ACDE BCDE
...
1 2 3 4 25 <- ABCE ABDE ACDE BCDE
1 2 3 5 6 <- ABDE ACDE BCDE
...
1 2 3 24 25 <- ABDE ACDE BCDE
1 2 4 5 6 <- ACDE BCDE
...
1 2 23 24 25 <- ACDE BCDE
1 3 4 5 6 <- BCDE
...
1 22 23 24 25 <- BCDE
2 3 4 5 6 <- none
...
21 22 23 24 25 <- none
三个部分的分区可以通过取[2,2,1]、[2,1,2]、[1,2,2]、[3,1,1]、[1,3,1]和[1,1,3] 来自这些三组组合的元素:
A B C D E
1 2 3 4 5 <- ABC ABD ACD BCD ABE ACE BCE ADE BDE CDE
1 2 3 4 6 <- ABE ACE BCE ADE BDE CDE
...
1 2 3 4 25 <- ABE ACE BCE ADE BDE CDE
1 2 3 5 6 <- ADE BDE CDE
...
1 2 3 24 25 <- ADE BDE CDE
1 2 4 5 6 <- CDE
...
1 2 23 24 25 <- CDE
1 3 4 5 6 <- none
...
21 22 23 24 25 <- none
可以通过从以下两组组合中获取 [2,3]、[3,2]、[4,1] 和 [1,4] 元素来整合具有两部分的分区:
A B C D E
1 2 3 4 5 <- AB AC BC AD BD CD AE BE CE DE
1 2 3 4 6 <- AE BE CE DE
...
1 2 3 4 25 <- AE BE CE DE
1 2 3 5 6 <- DE
...
1 2 3 24 25 <- DE
1 2 4 5 6 <- none
...
21 22 23 24 25 <- none
[1,1,1 ... 1] [2,1,1 ... 1] [2,2,1 ... 1] ... [k] (if k <= g)
[1,1,1 ... 1] [2,1,1 ... 1] [2,2,1 ... 1] ... [g,k-g] (if k > g)
对于其中的每一个,生成所有唯一的排列,例如:
[3,2,2,1] -> [3,2,2,1] [3,2,1,2] [3,1,2,2]
[2,3,2,1] [2,3,1,2] [1,3,2,2]
[2,2,3,1] [2,1,3,2] [1,2,3,2]
[2,2,1,3] [2,1,2,3] [1,2,2,3]
对每个部分的排列进行排序,例如:
k: [1,1,1 ... 1]
k-1: [2,1 ... 1] [1,2 ... 1] ... [1,1 ... 2]
...
2: [g,k-g] [k-g,g]
将前 k 个组加载到内存中,例如:
A B C D E F
1 2 3 4 5 6
对于分区 p 的每个长度,生成每组大小为 p 的组,例如:
p=k: ABCDEF C(k,k) sets
p=k-1: ABCDE ABCDF ABCEF ABDEF ACDEF BCDEF C(k,k-1) sets
p=k-2: ABCD ABCE ABCF ABDE ABDF ... CDEF C(k,k-2) sets
...
p=2: AB AC AD AE AF BC BD BE BF ... EF C(k,2) sets
对于这些集合中的每一个,生成具有相应部分数量的分区的组合,例如:
p=k-1: ABCDE [2,1,1,1,1] -> [a,a,b,c,d,e] C(g,2)*C(g,1)^4 combinations
[1,2,1,1,1] -> [a,b,b,c,d,e]
[1,1,2,1,1] -> [a,b,c,c,d,e]
[1,1,1,2,1] -> [a,b,c,d,d,e]
[1,1,1,1,2] -> [a,b,c,d,e,e]
ABCDE [2,1,1,1,1] -> [a,a,b,c,d,f]
[1,2,1,1,1] -> [a,b,b,c,d,f]
[1,1,2,1,1] -> [a,b,c,c,d,f]
[1,1,1,2,1] -> [a,b,c,d,d,f]
[1,1,1,1,2] -> [a,b,c,d,f,f]
...
BCDEF [2,1,1,1,1] -> [b,b,c,d,e,f]
[1,2,1,1,1] -> [b,c,c,d,e,f]
[1,1,2,1,1] -> [b,c,d,d,e,f]
[1,1,1,2,1] -> [b,c,d,e,e,f]
[1,1,1,1,2] -> [b,c,d,e,f,f]
从集合列表中,删除不包含最后一组 (F) 的集合:
p=k: ABCDEF
p=k-1: ABCDF ABCEF ABDEF ACDEF BCDEF
p=k-2: ABCF ABDF ABEF ACDF ACEF ADEF BCDF BCEF BDEF CDEF
...
p=2: AF BF CF DF EF
将下一组直到 e/g 作为组 F 加载到内存中,例如:
A B C D E F
1 2 3 4 5 7
...
1 2 3 4 5 e/g
同样,对于这些中的每一个,以及对于每个集合,生成具有相应部分数量的分区的组合。
p=k: ABCDEF
p=k-1: ABCEF ABDEF ACDEF BCDEF
p=k-2: ABEF ACEF ADEF BCEF BDEF CDEF
...
p=2: EF
将直到 e/g-1 的下一组作为 E 组加载到内存中,对于其中的每一个,将 E 到 e/g 之后的组作为 F 组加载到内存中,例如:
A B C D E F
1 2 3 4 6 7
...
1 2 3 4 e/g-1 e/g
同样,对于这些中的每一个,以及对于每个集合,生成具有相应部分数量的分区的组合。
p=k: ABCDEF
p=k-1: ABDEF ACDEF BCDEF
p=k-2: ADEF BDEF CDEF
...
p=2: none
将下一组直到 e/g-2 作为组 D 加载到内存中,对于每个组,将 D 到 e/g-1 之后的组加载到内存中作为 E 组,对于每个组,将组加载到内存中在 E 到 e/g 之后作为组 F 进入内存,例如:
A B C D E F
1 2 3 5 6 7
...
1 2 3 e/g-2 e/g-1 e/g
同样,对于这些中的每一个,以及对于每个集合,生成具有相应部分数量的分区的组合。
A B C D E F
e/g-5 e/g-4 e/g-3 e/g-2 e/g-1 e/g
只有:
p=k: ABCDEF
number of elements: e = 21
elements: [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]
size of combinations: k = 3 elements
size of memory: m = 9 elements
number of groups in memory: 3 (k)
group size: g = m/k = 3 elements
number of groups: e/g = 7
groups: 1:[1,2,3] 2:[4,5,6] 3:[7,8,9] 4:[10,11,12] 5:[13,14,15] 6:[16,17,18] 7:[19,20,21]
number of element sets loaded into memory: C(e/g,k) = C(7,3) = 35
partitions of k with max part g: [1,1,1] [2,1] [3]
permutations: 3:{[1,1,1]} 2:{[1,2],[2,1]} 1:{[3]}
group sets: 3:{[A,B,C]} 2:{[A,B],[A,C],[B,C]} 1:{[A],[B],[C]}
阶段1:
group sets: 3:{[A,B,C]} 2:{[A,B],[A,C],[B,C]} 1:{[A],[B],[C]} (all)
A B C
1 2 3 -> elements in memory: [1,2,3] [4,5,6] [7,8,9] -> 84 combinations
3: [1,1,1]:[A,B,C] -> [a,b,c] -> [1,4,7] [1,4,8] [1,4,9] [1,5,7] [1,5,8] [1,5,9] [1,6,7] [1,6,8] [1,6,9]
[2,4,7] [2,4,8] [2,4,9] [2,5,7] [2,5,8] [2,5,9] [2,6,7] [2,6,8] [2,6,9]
[3,4,7] [3,4,8] [3,4,9] [3,5,7] [3,5,8] [3,5,9] [3,6,7] [3,6,8] [3,6,9]
2: [1,2]:[A,B] -> [a,b,b] -> [1,4,5] [1,4,6] [1,5,6] [2,4,5] [2,4,6] [2,5,6] [3,4,5] [3,4,6] [3,5,6]
[1,2]:[A,C] -> [a,c,c] -> [1,7,8] [1,7,9] [1,8,9] [2,7,8] [2,7,9] [2,8,9] [3,7,8] [3,7,9] [3,8,9]
[1,2]:[B,C] -> [b,c,c] -> [4,7,8] [4,7,9] [4,8,9] [5,7,8] [5,7,9] [5,8,9] [6,7,8] [6,7,9] [6,8,9]
[2,1]:[A,B] -> [a,a,b] -> [1,2,4] [1,3,4] [2,3,4] [1,2,5] [1,3,5] [2,3,5] [1,2,6] [1,3,6] [2,3,6]
[2,1]:[A,C] -> [a,a,c] -> [1,2,7] [1,3,7] [2,3,7] [1,2,8] [1,3,8] [2,3,8] [1,2,9] [1,3,9] [2,3,9]
[2,1]:[B,C] -> [b,b,c] -> [4,5,7] [4,6,7] [5,6,7] [4,5,8] [4,6,8] [5,6,8] [4,5,9] [4,6,9] [5,6,9]
1: [3]:[A] -> [a,a,a] -> [1,2,3]
[3]:[B] -> [b,b,b] -> [4,5,6]
[3]:[C] -> [c,c,c] -> [7,8,9]
阶段2:
group sets: 3:{[A,B,C]} 2:{[A,C],[B,C]} 1:{[C]} (sets without C removed)
A B C
1 2 4 -> elements in memory: [1,2,3] [4,5,6] [10,11,12] -> 64 combinations
3: [1,1,1]:[A,B,C] -> [a,b,c] -> [1,4,10] [1,4,11] [1,4,12] [1,5,10] [1,5,11] [1,5,12] [1,6,10] [1,6,11] [1,6,12]
[2,4,10] [2,4,11] [2,4,12] [2,5,10] [2,5,11] [2,5,12] [2,6,10] [2,6,11] [2,6,12]
[3,4,10] [3,4,11] [3,4,12] [3,5,10] [3,5,11] [3,5,12] [3,6,10] [3,6,11] [3,6,12]
2: [1,2]:[A,C] -> [a,c,c] -> [1,10,11] [1,10,12] [1,11,12] [2,10,11] [2,10,12] [2,11,12] [3,10,11] [3,10,12] [3,11,12]
[1,2]:[B,C] -> [b,c,c] -> [4,10,11] [4,10,12] [4,11,12] [5,10,11] [5,10,12] [5,11,12] [6,10,11] [6,10,12] [6,11,12]
[2,1]:[A,C] -> [a,a,c] -> [1,2,10] [1,3,10] [2,3,10] [1,2,11] [1,3,11] [2,3,11] [1,2,12] [1,3,12] [2,3,12]
[2,1]:[B,C] -> [b,b,c] -> [4,5,10] [4,6,10] [5,6,10] [4,5,11] [4,6,11] [5,6,11] [4,5,12] [4,6,12] [5,6,12]
1: [3]:[C] -> [c,c,c] -> [10,11,12]
A B C
1 2 5 -> elements in memory: [1,2,3] [4,5,6] [13,14,15] -> 64 combinations
1 2 6 -> elements in memory: [1,2,3] [4,5,6] [16,17,18] -> 64 combinations
1 2 7 -> elements in memory: [1,2,3] [4,5,6] [19,20,21] -> 64 combinations
第 3 阶段:
group sets: 3:{[A,B,C]} 2:{[B,C]} (sets without B removed)
A B C
1 3 4 -> elements in memory: [1,2,3] [7,8,9] [10,11,12] -> 45 combinations
3: [1,1,1]:[A,B,C] -> [a,b,c] -> [1,7,10] [1,7,11] [1,7,12] [1,8,10] [1,8,11] [1,8,12] [1,9,10] [1,9,11] [1,9,12]
[2,7,10] [2,7,11] [2,7,12] [2,8,10] [2,8,11] [2,8,12] [2,9,10] [2,9,11] [2,9,12]
[3,7,10] [3,7,11] [3,7,12] [3,8,10] [3,8,11] [3,8,12] [3,9,10] [3,9,11] [3,9,12]
2: [1,2]:[B,C] -> [b,c,c] -> [7,10,11] [7,10,12] [7,11,12] [8,10,11] [8,10,12] [8,11,12] [9,10,11] [9,10,12] [9,11,12]
[2,1]:[B,C] -> [b,b,c] -> [7,8,10] [7,9,10] [8,9,10] [7,8,11] [7,9,11] [8,9,11] [7,8,12] [7,9,12] [8,9,12]
A B C
1 3 5 -> elements in memory: [1,2,3] [7,8,9] [13,14,15] -> 45 combinations
1 3 6 -> elements in memory: [1,2,3] [7,8,9] [16,17,18] -> 45 combinations
1 3 7 -> elements in memory: [1,2,3] [7,8,9] [19,20,21] -> 45 combinations
1 4 5 -> elements in memory: [1,2,3] [7,8,9] [13,14,15] -> 45 combinations
1 4 6 -> elements in memory: [1,2,3] [7,8,9] [16,17,18] -> 45 combinations
1 4 7 -> elements in memory: [1,2,3] [7,8,9] [19,20,21] -> 45 combinations
1 5 6 -> elements in memory: [1,2,3] [7,8,9] [16,17,18] -> 45 combinations
1 5 7 -> elements in memory: [1,2,3] [7,8,9] [19,20,21] -> 45 combinations
1 6 7 -> elements in memory: [1,2,3] [7,8,9] [19,20,21] -> 45 combinations
第 4 阶段:
group sets: 3:{[A,B,C]} (sets without A removed)
A B C
2 3 4 -> elements in memory: [4,5,6] [7,8,9] [10,11,12] -> 27 combinations
3: [1,1,1]:[A,B,C] -> [a,b,c] -> [4,7,10] [4,7,11] [4,7,12] [4,8,10] [4,8,11] [4,8,12] [4,9,10] [4,9,11] [4,9,12]
[5,7,10] [5,7,11] [5,7,12] [5,8,10] [5,8,11] [5,8,12] [5,9,10] [5,9,11] [5,9,12]
[6,7,10] [6,7,11] [6,7,12] [6,8,10] [6,8,11] [6,8,12] [6,9,10] [6,9,11] [6,9,12]
A B C
2 3 5 -> elements in memory: [4,5,6] [7,8,9] [13,14,15] -> 27 combinations
2 3 6 -> elements in memory: [4,5,6] [7,8,9] [16,17,18] -> 27 combinations
2 3 7 -> elements in memory: [4,5,6] [7,8,9] [19,20,21] -> 27 combinations
2 4 5 -> elements in memory: [4,5,6] [10,11,12] [13,14,15] -> 27 combinations
2 4 6 -> elements in memory: [4,5,6] [10,11,12] [16,17,18] -> 27 combinations
2 4 7 -> elements in memory: [4,5,6] [10,11,12] [19,20,21] -> 27 combinations
2 5 6 -> elements in memory: [4,5,6] [13,14,15] [16,17,18] -> 27 combinations
2 5 7 -> elements in memory: [4,5,6] [13,14,15] [19,20,21] -> 27 combinations
2 6 7 -> elements in memory: [4,5,6] [16,17,18] [19,20,21] -> 27 combinations
3 4 5 -> elements in memory: [7,8,9] [10,11,12] [13,14,15] -> 27 combinations
3 4 6 -> elements in memory: [7,8,9] [10,11,12] [16,17,18] -> 27 combinations
3 4 7 -> elements in memory: [7,8,9] [10,11,12] [19,20,21] -> 27 combinations
3 5 6 -> elements in memory: [7,8,9] [13,14,15] [16,17,18] -> 27 combinations
3 5 7 -> elements in memory: [7,8,9] [13,14,15] [19,20,21] -> 27 combinations
3 6 7 -> elements in memory: [7,8,9] [16,17,18] [19,20,21] -> 27 combinations
4 5 6 -> elements in memory: [10,11,12] [13,14,15] [16,17,18] -> 27 combinations
4 5 7 -> elements in memory: [10,11,12] [13,14,15] [19,20,21] -> 27 combinations
4 6 7 -> elements in memory: [10,11,12] [16,17,18] [19,20,21] -> 27 combinations
5 6 7 -> elements in memory: [13,14,15] [16,17,18] [19,20,21] -> 27 combinations
结果:
Phase 1: 84 = 84 combinations
Phase 2: 4 x 64 = 256 combinations
Phase 3: 10 x 45 = 450 combinations
Phase 4: 20 x 27 = 540 combinations
----
1330 combinations = C(21,3)
关于algorithm - 如何生成 block 中的组合,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46635137/
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