# A symmetric matrix multiplied by a scalar is not symmetric

**URL:** <https://discourse.julialang.org/t/a-symmetric-matrix-multiplied-by-a-scalar-is-not-symmetric/22894>\
**Category:** New to Julia\
**Created:** [April 7, 2019, 11:18pm UTC](https://discourse.julialang.org/t/a-symmetric-matrix-multiplied-by-a-scalar-is-not-symmetric/22894 "2019-04-07T23:18:28Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Marco-Congedo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marco-congedo/32/7321_2.png) [@Marco-Congedo](https://discourse.julialang.org/u/Marco-Congedo)\
**Post date:** [April 7, 2019, 11:18pm UTC](https://discourse.julialang.org/t/a-symmetric-matrix-multiplied-by-a-scalar-is-not-symmetric/22894/1 "2019-04-07T23:18:28Z")

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Hello,  
I have a Symmetric matrix P. When i post-multiply it by a scalar it is still Symmetric, but when i pre-multiply it with the same scalar it is no more Symmetric. Why julia does that ?  
Here is an example, the same happens for Hermitian matrices.  
I am running Julia Version 1.0.3

julia\> P  
3×3 Symmetric{Float64,Array{Float64,2}}:  
1.5441 -1.04908 0.225946  
-1.04908 3.39796 -0.193123  
0.225946 -0.193123 2.72884

julia\> P\*2  
3×3 Symmetric{Float64,Array{Float64,2}}:  
3.08821 -2.09816 0.451892  
-2.09816 6.79592 -0.386245  
0.451892 -0.386245 5.45768

julia\> 2\*P  
3×3 Array{Float64,2}:  
3.08821 -2.09816 0.451892  
-2.09816 6.79592 -0.386245  
0.451892 -0.386245 5.45768

---

<div class="post-metadata">

**Author:** ![sagartewari01](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sagartewari01/32/7810_2.png) [@sagartewari01](https://discourse.julialang.org/u/sagartewari01)\
**Post date:** [April 7, 2019, 11:27pm UTC](https://discourse.julialang.org/t/a-symmetric-matrix-multiplied-by-a-scalar-is-not-symmetric/22894/2 "2019-04-07T23:27:25Z")

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Appears to be fixed on julia-1.1.0.

```julia
> julia
               _
   _ _ _(_)_ | Documentation: https://docs.julialang.org
  (_) | (_) (_) |
   _ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` | |
  | | |_| | | | (_| | | Version 1.1.0 (2019-01-21)
 _/ |\ __'_|_|_|\__'_| |
|__/ |

julia> using LinearAlgebra

julia> s = Symmetric(rand(3,3))
3×3 Symmetric{Float64,Array{Float64,2}}:
 0.0793429 0.681884 0.364857
 0.681884 0.212794 0.790376
 0.364857 0.790376 0.555614

julia> 2*s
3×3 Symmetric{Float64,Array{Float64,2}}:
 0.158686 1.36377 0.729715
 1.36377 0.425589 1.58075
 0.729715 1.58075 1.11123

julia> s*2
3×3 Symmetric{Float64,Array{Float64,2}}:
 0.158686 1.36377 0.729715
 1.36377 0.425589 1.58075
 0.729715 1.58075 1.11123

```

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<div class="post-metadata">

**Author:** ![Marco-Congedo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marco-congedo/32/7321_2.png) [@Marco-Congedo](https://discourse.julialang.org/u/Marco-Congedo)\
**Post date:** [April 8, 2019, 12:15pm UTC](https://discourse.julialang.org/t/a-symmetric-matrix-multiplied-by-a-scalar-is-not-symmetric/22894/3 "2019-04-08T12:15:48Z")

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Thanks, i will check out the new version then.