# Error matrix infinity norm
**URL:** https://discourse.julialang.org/t/error-matrix-infinity-norm/14600
**Category:** General Usage
**Created:** [September 6, 2018, 12:08am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600 "2018-09-06T00:08:13Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@OlivierHnt](https://discourse.julialang.org/u/OlivierHnt)
#### Post date: [September 6, 2018, 12:08am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600/1 "2018-09-06T00:08:14Z")
Hello,
I was having a hard time trying to debug a code today, but it turns out the problem came from the function `norm` itself. The infinity norm of a matrix is not correct in Julia. According to Julia `norm(A,Inf) = max(abs.(A))`, that is it returns the largest element in `abs.(A)`.
(Note: might be worth to check that the one norm works too then. I will check later tonight).
Is this issue known ? I never saw any comments about it. If it is not, who should be contacted ?
If it is known but not yet corrected, is there a simple fix ? (by “fix” I mean fixing the function itself not how to write a code to compute the infinity norm).
I tried `Pkg.update("LinearAlgebra")` but apparently nothing new.
Thank you for your help!
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### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [September 6, 2018, 1:05am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600/2 "2018-09-06T01:05:38Z")
What do you think the correct result should be?
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### Author:  [@dpsanders](https://discourse.julialang.org/u/dpsanders)
#### Post date: [September 6, 2018, 1:07am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600/3 "2018-09-06T01:07:36Z")
I am no expert, but Wikipedia seems to agree with Julia (“max norm”) :
> **[Matrix norm](https://en.m.wikipedia.org/wiki/Matrix_norm)**
>
> In mathematics, a matrix norm is a vector norm in a vector space whose elements (vectors) are matrices (of given dimensions).
> Given a field
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> K
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> {\\displaystyle K}
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> of either real or complex numbers, let
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> K
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> m
> ×
> n
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> {\\displaystyle K^{m\\times n}}
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> be the K-vector space of matrices with
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> m
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> {\\displaystyle m...
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### Author:  [@Pbellive](https://discourse.julialang.org/u/Pbellive)
#### Post date: [September 6, 2018, 1:22am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600/4 "2018-09-06T01:22:56Z")
What version of Julia are you using? Looks like things have changed from 0.6 to 1.0. According to the 0.6 docs for the norm function, `norm(A,Inf)` should give the matrix norm induced by the vector infinity norm, so the maximum row sum of A rather than just the entry with largest absolute value. However, in 1.0 the `norm` function just treats a matrix as if it were a vector of all the entries. You now need to use the new function `opnorm` for matrix norms induced by vector norms. E.g. on 1.0 I get
```julia
julia> A = [1 2;3 4]
2×2 Array{Int64,2}:
1 2
3 4
julia> norm(A,Inf)
4.0
julia> opnorm(A,Inf)
7.0
```
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### Author:  [@OlivierHnt](https://discourse.julialang.org/u/OlivierHnt)
#### Post date: [September 6, 2018, 1:31am UTC](https://discourse.julialang.org/t/error-matrix-infinity-norm/14600/5 "2018-09-06T01:31:29Z")
Oh I see, I should be using `opnorm(A,Inf)` then! Thank you very much.