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Documentation mynorm should not divide by n #29091

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merged 1 commit into from
Sep 8, 2018

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dehann
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@dehann dehann commented Sep 7, 2018

Test with:

a = randn(10)
abs(norm(a) - mynorm(a)) < 1e10

Tested here:

   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.6.4 (2018-07-09 19:09 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> function mynorm(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s)
       end
mynorm (generic function with 1 method)

julia> function mynorm_old(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s/n)
       end
mynorm_old (generic function with 1 method)

julia> a = randn(10)
10-element Array{Float64,1}:
 -0.564163
 -3.45236 
 -0.50901 
 -0.030296
  0.114156
  0.661961
 -1.19972 
  2.20883 
  1.74529 
  0.82515 

julia> abs(norm(a)-mynorm(a))
0.0

julia> abs(norm(a)-mynorm_old(a))
3.2787896367314344

Test with:
```julia
a = randn(10)
abs(norm(a) - mynorm(a)) < 1e10
```

Tested here:
```julia-repl
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.6.4 (2018-07-09 19:09 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> function mynorm(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s)
       end
mynorm (generic function with 1 method)

julia> function mynorm_old(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s/n)
       end
mynorm_old (generic function with 1 method)

julia> a = randn(10)
10-element Array{Float64,1}:
 -0.564163
 -3.45236 
 -0.50901 
 -0.030296
  0.114156
  0.661961
 -1.19972 
  2.20883 
  1.74529 
  0.82515 

julia> abs(norm(a)-mynorm(a))
0.0

julia> abs(norm(a)-mynorm_old(a))
3.2787896367314344
```
@andreasnoack andreasnoack merged commit a572504 into JuliaLang:master Sep 8, 2018
@fredrikekre fredrikekre added docs This change adds or pertains to documentation backport pending 1.0 labels Sep 8, 2018
KristofferC pushed a commit that referenced this pull request Sep 10, 2018
Test with:
```julia
a = randn(10)
abs(norm(a) - mynorm(a)) < 1e10
```

Tested here:
```julia-repl
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.6.4 (2018-07-09 19:09 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> function mynorm(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s)
       end
mynorm (generic function with 1 method)

julia> function mynorm_old(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s/n)
       end
mynorm_old (generic function with 1 method)

julia> a = randn(10)
10-element Array{Float64,1}:
 -0.564163
 -3.45236
 -0.50901
 -0.030296
  0.114156
  0.661961
 -1.19972
  2.20883
  1.74529
  0.82515

julia> abs(norm(a)-mynorm(a))
0.0

julia> abs(norm(a)-mynorm_old(a))
3.2787896367314344
```

(cherry picked from commit a572504)
@KristofferC KristofferC mentioned this pull request Sep 10, 2018
KristofferC pushed a commit that referenced this pull request Feb 11, 2019
Test with:
```julia
a = randn(10)
abs(norm(a) - mynorm(a)) < 1e10
```

Tested here:
```julia-repl
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.6.4 (2018-07-09 19:09 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-pc-linux-gnu

julia> function mynorm(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s)
       end
mynorm (generic function with 1 method)

julia> function mynorm_old(u::Vector)
           n = length(u)
           T = eltype(u)
           s = zero(T)
           @fastmath @inbounds @simd for i in 1:n
               s += u[i]^2
           end
           @fastmath @inbounds return sqrt(s/n)
       end
mynorm_old (generic function with 1 method)

julia> a = randn(10)
10-element Array{Float64,1}:
 -0.564163
 -3.45236
 -0.50901
 -0.030296
  0.114156
  0.661961
 -1.19972
  2.20883
  1.74529
  0.82515

julia> abs(norm(a)-mynorm(a))
0.0

julia> abs(norm(a)-mynorm_old(a))
3.2787896367314344
```

(cherry picked from commit a572504)
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4 participants