# CUDA.rand() returns duplicate columns

**URL:** <https://discourse.julialang.org/t/cuda-rand-returns-duplicate-columns/63993>\
**Category:** GPU\
**Created:** [July 3, 2021, 4:35pm UTC](https://discourse.julialang.org/t/cuda-rand-returns-duplicate-columns/63993 "2021-07-03T16:35:07Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![jpdoane](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jpdoane](https://discourse.julialang.org/u/jpdoane)\
**Post date:** [July 3, 2021, 4:35pm UTC](https://discourse.julialang.org/t/cuda-rand-returns-duplicate-columns/63993/1 "2021-07-03T16:35:07Z")

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CUDA.rand() appears to return duplicate columns of complex numbers:

```julia
julia> CUDA.rand(ComplexF32, 512, 3)
512×3 CuArray{ComplexF32, 2}:
 0.831271+0.460309im 0.831271+0.460309im 0.831271+0.460309im
 0.0160654+0.0647557im 0.0160654+0.0647557im 0.0160654+0.0647557im
 0.457093+0.979712im 0.457093+0.979712im 0.457093+0.979712im
 0.586642+0.25824im 0.586642+0.25824im 0.586642+0.25824im
 0.0836292+0.925833im 0.0836292+0.925833im 0.0836292+0.925833im
 0.816079+0.822063im 0.816079+0.822063im 0.816079+0.822063im
...

```

I did not observe this behavior when using real numbers.  
I am running julia 1.6.1, CUDA.jl v3.3.1, and CUDA 11.4

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<div class="post-metadata">

**Author:** ![genkuroki](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/genkuroki/32/18030_2.png) [@genkuroki](https://discourse.julialang.org/u/genkuroki)\
**Post date:** [July 3, 2021, 5:21pm UTC](https://discourse.julialang.org/t/cuda-rand-returns-duplicate-columns/63993/2 "2021-07-03T17:21:29Z")

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I have the same problem on Windows 10.

- Julia v1.8.0-DEV.94
- CUDA v3.3.2
- CUDA driver 11.2.0
- NVIDIA driver 462.31.0
- GeForce GTX 1650 Ti

```julia
julia> a = CUDA.rand(ComplexF32, 1024);

julia> minimum(k for k in 1:1023 if a[1] == a[1+k])
256

julia> [a[1+256k] for k in 0:3]
4-element Vector{ComplexF32}:
 0.3636915f0 + 0.4992487f0im
 0.3636915f0 + 0.4992487f0im
 0.3636915f0 + 0.4992487f0im
 0.3636915f0 + 0.4992487f0im

julia> all(all(a[i] == a[i+256k] for k in 1:3) for i in 1:256)
true

```

The period is 2^8.

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<div class="post-metadata">

**Author:** ![maleadt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maleadt/32/10097_2.png) [@maleadt](https://discourse.julialang.org/u/maleadt)\
**Post date:** [July 3, 2021, 8:51pm UTC](https://discourse.julialang.org/t/cuda-rand-returns-duplicate-columns/63993/3 "2021-07-03T20:51:34Z")

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Looks like a bug in the GPUArrays RNG – for reals CURAND is used. Please file an issue, we might be able to use the new CUDA RNG for this (`CUDA.RNG()`), which is built on RandomNumber.jl. But from a quick glance ComplexF32 numbers aren’t supported by that package out of the box.