Merge d2ada3d into 6bd561c

NEWS.md

@@ -1,5 +1,12 @@
 # History of Measurements.jl
 
+## v2.7.2 (2022-0?-??)
+
+### Bug Fixes
+
+* Fixed norm of `AbstractArray{<:Measurement}`
+  ([#120](https://github.com/JuliaPhysics/Measurements.jl/pull/120)).
+
 ## v2.7.1 (2022-03-03)
 
 ### Bug Fixes

src/Measurements.jl

@@ -122,6 +122,7 @@ include("conversions.jl")
 include("comparisons-tests.jl")
 include("utils.jl")
 include("math.jl")
+include("linear_algebra.jl")
 include("show.jl")
 include("parsing.jl")
 include("plot-recipes.jl")

src/linear_algebra.jl

@@ -0,0 +1,14 @@
+using LinearAlgebra
+
+function LinearAlgebra.normInf(A::AbstractArray{<:Measurement})
+    norm = LinearAlgebra.generic_normInf(A)
+    if iszero(norm.val)
+        # This is a bit complicated, follow me.  The Inf-norm is the limit of the p-norms,
+        # for `p > 1`.  But for `p > 1` we always have `(0 ± u) ^ p == 0 ± 0`, for any value
+        # of `u` so the limit is always `0 ± 0`, in particular the uncertainty is always
+        # zero.  Therefore, if the the maximum absolute value is zero, then also the
+        # uncertainty must be zero, whatever were the other uncertainties.
+        return zero(norm)
+    end
+    return norm
+end

test/runtests.jl

@@ -728,6 +728,19 @@ end
     @test @inferred(b ⋅ c) ≈ 7.020527859237536 ± 0.5707235338984873
     @test @inferred(det(A)) ≈ 682 ± 9.650906693155829
     @test @inferred(A * inv(A)) ≈ I
+    # This matrix `A` has the property that the Inf-norm of `A * inv(A) - I` has
+    # zero value but non-zero uncertainty in Julia v1.9, which would make the
+    # check `A * inv(A) ≈ I` fail.
+    A = [(14 ± 0.1) (23 ± 0.2); (-12 ± 0.3) (24 ± 0.4)]
+    @test @inferred(norm(A * inv(A) - I)) ≈ zero(Measurement{Float64}) atol=3e-16
+    @test @inferred(A * inv(A)) ≈ I
+
+    Z = [(0 ± 1) (0 ± 2); (0 ± 3) (0 ± 4)]
+    @test norm(Z, 0) == 4 ± 0 # Note: all elements of `Z` are `!iszero`
+    @test norm(Z, 1) == 0 ± sqrt(sum(abs2, uncertainty.(Z)))
+    @test norm(Z, 2) == zero(Measurement{Float64})
+    @test norm(Z, 5) == zero(Measurement{Float64})
+    @test norm(Z, Inf) == zero(Measurement{Float64})
 end
 
 @testset "NaNs" begin