# Multiply the first column of a matrix by several different scalars
**URL:** https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897
**Category:** New to Julia
**Created:** [April 2, 2020, 10:28am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897 "2020-04-02T10:28:40Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@samantp](https://discourse.julialang.org/u/samantp)
#### Post date: [April 2, 2020, 10:28am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/1 "2020-04-02T10:28:40Z")
I have a matrix, `A`, which is of size nx2 and a vector, `v`, of 1000 coefficients.
I would like to create a vector of arrays, `A_mult` which has 1000 elements, such that every entry in A\_mult consists of A with the first column multiplied by a corresponding entry of v.
i.e.
```julia
A_mult[1][:,1]=A[:,1]*v[1]
A_mult[1][:,2]=A[:,2]
A_mult[2][:,1]=A[:,1]*v[2]
A_mult[2][:,2]=A[:,2]
```
…etc
so essentially I want the first column of A to be multiplied by all the entries in v, and then store the resulting matrices in a new array. Is it possible to do this without a loop?
Thanks
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### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [April 2, 2020, 10:39am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/2 "2020-04-02T10:39:10Z")
Out of curiosity, why do you need to avoid a loop? Seems like it would be a bit cumbersome.
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### Author:  [@samantp](https://discourse.julialang.org/u/samantp)
#### Post date: [April 2, 2020, 10:45am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/3 "2020-04-02T10:45:31Z")
I suppose I don’t, I was just under the impression that this might not be as efficient as compared to a vectorized form
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### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [April 2, 2020, 10:59am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/4 "2020-04-02T10:59:11Z")
No, that’s incorrect. Loops are normally the fastest way.
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### Author:  [@samantp](https://discourse.julialang.org/u/samantp)
#### Post date: [April 2, 2020, 11:00am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/5 "2020-04-02T11:00:31Z")
Good to know! Loops it is then!
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### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [April 2, 2020, 11:03am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/6 "2020-04-02T11:03:47Z")
Matlab, R and Python, etc. have slow loops, while Julia has fast loops, like C or Fortran.
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### Author:  [@mcabbott](https://discourse.julialang.org/u/mcabbott)
#### Post date: [April 2, 2020, 11:15am UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/7 "2020-04-02T11:15:09Z")
I think you can just write `[A .* [s,1]' for s in v]`.
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### Author:  [@dmolina](https://discourse.julialang.org/u/dmolina)
#### Post date: [April 2, 2020, 1:14pm UTC](https://discourse.julialang.org/t/multiply-the-first-column-of-a-matrix-by-several-different-scalars/36897/8 "2020-04-02T13:14:03Z")
You should use a loop as other people have said, in Julia the loops are very quickly. Also, you could be interested also in [GitHub - JuliaSIMD/LoopVectorization.jl: Macro(s) for vectorizing loops.](https://github.com/chriselrod/LoopVectorization.jl.git).