# Training with Mutating Arrays

**URL:** <https://discourse.julialang.org/t/training-with-mutating-arrays/91876>\
**Category:** New to Julia\
**Tags:** neural-network, training\
**Created:** [December 19, 2022, 10:59pm UTC](https://discourse.julialang.org/t/training-with-mutating-arrays/91876 "2022-12-19T22:59:24Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [December 20, 2022, 7:45am UTC](https://discourse.julialang.org/t/training-with-mutating-arrays/91876/2 "2022-12-20T07:45:18Z")

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> [@ChrisVL1](#):
>
> ```julia
> for i = 1:length(K)
> NSDE_call[i] = exp(-r*tspan[2]).*mean(maximum([terminal_values .- K[i] zeros(size(terminal_values))], dims = 2))
> end 
> 
> ```

Just don’t mutate an array and the error saying you shouldn’t mutate an array will disappear. Change that to:

```julia
NSDE_call = map(i->exp(-r*tspan[2]).*mean(maximum([terminal_values .- K[i] zeros(size(terminal_values))], dims = 2),1:length(K))

```

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