# A question about fft function

**URL:** <https://discourse.julialang.org/t/a-question-about-fft-function/42026>\
**Category:** Optimization (Mathematical)\
**Tags:** question\
**Created:** [June 25, 2020, 7:13am UTC](https://discourse.julialang.org/t/a-question-about-fft-function/42026 "2020-06-25T07:13:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![abcde](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/abcde/32/16180_2.png) [@abcde](https://discourse.julialang.org/u/abcde)\
**Post date:** [June 25, 2020, 7:13am UTC](https://discourse.julialang.org/t/a-question-about-fft-function/42026/1 "2020-06-25T07:13:22Z")

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![image](https://global.discourse-cdn.com/julialang/original/3X/e/6/e6e5bff566582addc79aa6e2c0798b5d1a593a67.png)  
it does not work ,why?

```julia
a=[1 ,2 ,3 ,4]
b=[7 8 9 5]
foo=x->fft(x,2)
foo.(b)
#print(fft(b,2))

```

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**Author:** ![magister-ludi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/magister-ludi/32/4003_2.png) [@magister-ludi](https://discourse.julialang.org/u/magister-ludi)\
**Post date:** [June 25, 2020, 7:24am UTC](https://discourse.julialang.org/t/a-question-about-fft-function/42026/2 "2020-06-25T07:24:25Z")

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It’s not clear what you really want to do. `foo.(b)`, written with the dot, is asking `foo`, and thus `fft`, to act _element_-wise on `b`, but `fft` requires an `Array` argument.