# Weird behaviour of Identity matrix with symbolic type

**URL:** <https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186>\
**Category:** General Usage\
**Created:** [April 6, 2023, 3:52pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186 "2023-04-06T15:52:45Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![DerongXu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/derongxu/32/23102_2.png) [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Post date:** [April 6, 2023, 3:52pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/1 "2023-04-06T15:52:45Z")

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Hi all,

I’m utilizing SymPy within Julia to perform symbolic calculations, but I’ve noticed that the symbolic identity matrix operation is producing inaccurate outcomes. Can you explain why this is happening?

Please find the details in the attached picture.

![image](https://global.discourse-cdn.com/julialang/original/3X/f/b/fbdafd72e29a56afa8218737b3556120695b8219.png)

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<div class="post-metadata">

**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [April 6, 2023, 4:26pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/2 "2023-04-06T16:26:34Z")

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Odd, I don’t see this:

```julia
julia> using SymPy

julia> using LinearAlgebra

julia> B = Sym[1 2; 3 4]
2×2 Matrix{Sym}:
 1 2
 3 4

julia> I - B
2×2 Matrix{Sym}:
  0 -2
 -3 -3

```

Does it happen with a fresh session?

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<div class="post-metadata">

**Author:** ![DerongXu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/derongxu/32/23102_2.png) [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Post date:** [April 6, 2023, 5:39pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/3 "2023-04-06T17:39:52Z")

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Yes. I got different output.

julia\> using SymPy

julia\> using LinearAlgebra

julia\> B = Sym[1 2; 3 4]  
2×2 Matrix{Sym}:  
1 2  
3 4

julia\> I - B  
2×2 Matrix{Sym}:  
0 2  
3 3

julia\>

julia\>

---

<div class="post-metadata">

**Author:** ![DerongXu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/derongxu/32/23102_2.png) [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Post date:** [April 6, 2023, 5:42pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/4 "2023-04-06T17:42:03Z")

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and my julia version is

julia\> VERSION  
v"1.6.5"

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<div class="post-metadata">

**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [April 6, 2023, 7:32pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/5 "2023-04-06T19:32:18Z")

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I only have 1.6 installed on my machine, but this worked:

```julia
  | | |_| | | | (_| | | Version 1.6.0 (2021-03-24)
 _/ |\ __'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia> using SymPy, LinearAlgebra
[Info: Precompiling SymPy [24249f21-da20-56a4-8eb1-6a02cf4ae2e6]

julia> I - Sym[1 2; 3 4]
2×2 Matrix{Sym}:
  0 -2
 -3 -3

```

Which version of SymPy do you have?

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<div class="post-metadata">

**Author:** ![DerongXu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/derongxu/32/23102_2.png) [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Post date:** [April 6, 2023, 9:58pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/7 "2023-04-06T21:58:05Z")

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SymPy v1.0.47

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<div class="post-metadata">

**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [April 6, 2023, 10:06pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/8 "2023-04-06T22:06:33Z")

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That is a bit old, maybe upgrading will fix this?

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<div class="post-metadata">

**Author:** ![DerongXu](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/derongxu/32/23102_2.png) [@DerongXu](https://discourse.julialang.org/u/DerongXu)\
**Post date:** [April 21, 2023, 2:20pm UTC](https://discourse.julialang.org/t/weird-behaviour-of-identity-matrix-with-symbolic-type/97186/9 "2023-04-21T14:20:27Z")

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Thanks for your suggestion. The problem is fixed after the upgrading.