# EvalSum on a vector with 4000+ values

**URL:** <https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790>\
**Category:** Library Questions\
**Tags:** openfhe-help\
**Created:** [December 19, 2024, 2:58pm UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790 "2024-12-19T14:58:19Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![DenisRed](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/denisred/32/303_2.png) [@DenisRed](https://openfhe.discourse.group/u/DenisRed)\
**Post date:** [December 19, 2024, 2:58pm UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/1 "2024-12-19T14:58:20Z")

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Hi everyone,

im trying to use the `EvalSum()` operation on a vector with 4000+ values. Since this operation is based on several vector rotations, I have created rotation keys for all indices accordingly. The problem, however, is that the operation `EvalRotateKeyGen()` consumes so much memory that the program is killed with exit code 137.

What i want to achieve is going from this vector:

`vector<double> v1 = {51.2271, 6.61748e-13, 3.24305e-13, -1.57976e-13, -5.11591e-13, 9.34338e-13, 5.28346e-13, -9.16319e-14, ...}; // 4000+ values`

to this vector:

`vector<double> v2 = {51.2271, 51.2271, 51.2271, 51.2271, 51.2271, 51.2271, 51.2271, ...};`

I’m able to achieve that for vector with size 128. But with size 256 `EvalRotateKeyGen()` for an index list with 256 indices it rans out of memory. My pseudo code looks like this so far:

```auto
vector<double> mask(values.size(), 0);
mask[0] = 1;
auto ct = cc->EvalMult(cc->MakeCKKSPackedPlaintext(mask, 1, 0, nullptr, slots), v1);
auto ct2 = cc->EvalSum(ct, slots); // v2

```

This works for a value vector size of 128. Everything above is killed with code 137.

Is there a more efficient method to get from `v1` to `v2` ??

Thanks in advance! =)

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**Author:** ![andreea.alexandru](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/andreea.alexandru/32/378_2.png) [@andreea.alexandru](https://openfhe.discourse.group/u/andreea.alexandru)\
**Post date:** [December 19, 2024, 3:50pm UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/2 "2024-12-19T15:50:18Z")

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You should use EvalSumKeyGen, which generates a logarithmic number of rotation keys rather than one key for every index, or generate those keys yourself. EvalSum takes a logarithmic approach for efficiency reasons. Specifically, instead of computing ct2 = \sum\_{i=0}^{n-1} Rot(ct, i), it performs  
ct2 = ct;\\ For (i=0; i\< ceil(\log\_2(n)); ++i) \\ \quad ct2~ += ~Rot(ct2, 2^i)

Note that with this approach, you require only ceil(\log\_2(n))-1 instead of n-1 rotation keys.

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**Author:** ![DenisRed](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/denisred/32/303_2.png) [@DenisRed](https://openfhe.discourse.group/u/DenisRed)\
**Post date:** [December 20, 2024, 10:35am UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/3 "2024-12-20T10:35:20Z")

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Yeah i used this before but the error says: _EvalKey for index [625] is not found._  
Somehow it does not use the EvalSumKeys. Can you tell me how to use `EvalSum()` correctly with the generated keys of `EvalSumKeyGen()`?

```auto
auto evalSumKeys = cc->GetEvalSumKeyMap(kp.secretKey->GetKeyTag());
auto ct2 = cc->EvalSum(ct, slots, evalSumKeys); 
// Function has 2 parameters, but is called with 3 arguments
// only 2 arguments are accepted here?? The doc says i can add the key map as 3rd argument

```

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**Author:** ![ypolyakov](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/ypolyakov/32/47_2.png) [@ypolyakov](https://openfhe.discourse.group/u/ypolyakov)\
**Post date:** [December 21, 2024, 12:41am UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/4 "2024-12-21T00:41:29Z")

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It is hard to comment on it w/o seeing a minimal working example. `EvalSumKeyGen` uses the batchSize parameter. If it is set to 0 (default), then all keys should be generated (for maximum number of slots). If it is set to a smaller number, then not all keys will be generated.

Either way, it is hard to tell what is wrong w/o looking at a working example.

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<div class="post-metadata">

**Author:** ![andreea.alexandru](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/andreea.alexandru/32/378_2.png) [@andreea.alexandru](https://openfhe.discourse.group/u/andreea.alexandru)\
**Post date:** [December 23, 2024, 7:34pm UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/5 "2024-12-23T19:34:23Z")

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Maybe this example here will help you [Is there any example about how to use EvalSumRows/EvalSumCols? - #2 by Caesar](https://openfhe.discourse.group/t/is-there-any-example-about-how-to-use-evalsumrows-evalsumcols/687/2).

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<div class="post-metadata">

**Author:** ![DenisRed](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/denisred/32/303_2.png) [@DenisRed](https://openfhe.discourse.group/u/DenisRed)\
**Post date:** [December 30, 2024, 8:58am UTC](https://openfhe.discourse.group/t/evalsum-on-a-vector-with-4000-values/1790/6 "2024-12-30T08:58:52Z")

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Thanks! I didn’t know that `EvalSumKeyGen` uses the batchsize parameter. That solved my problem =)