From dfd70754f93ba043b9c1d4460183810ea51205f6 Mon Sep 17 00:00:00 2001
From: Lorenzo Stella <lorenzostella@gmail.com>
Date: Fri, 11 Mar 2022 20:44:58 +0100
Subject: [PATCH] Fix: allow weights in SqrNormL2 to be zero (#140)

---
 src/functions/sqrNormL2.jl | 16 ++++++++--------
 test/test_calls.jl         |  1 +
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/functions/sqrNormL2.jl b/src/functions/sqrNormL2.jl
index 546800e..0069c59 100644
--- a/src/functions/sqrNormL2.jl
+++ b/src/functions/sqrNormL2.jl
@@ -5,20 +5,20 @@ export SqrNormL2
 """
     SqrNormL2(λ=1)
 
-With a positive scalar `λ`, return the squared Euclidean norm
+With a nonnegative scalar `λ`, return the squared Euclidean norm
 ```math
 f(x) = \\tfrac{λ}{2}\\|x\\|^2.
 ```
-With a positive array `λ`, return the weighted squared Euclidean norm
+With a nonnegative array `λ`, return the weighted squared Euclidean norm
 ```math
 f(x) = \\tfrac{1}{2}∑_i λ_i x_i^2.
 ```
 """
-struct SqrNormL2{T}
+struct SqrNormL2{T,SC}
     lambda::T
-    function SqrNormL2{T}(lambda::T) where T
-        if any(lambda .<= 0)
-            error("coefficients in λ must be positive")
+    function SqrNormL2{T,SC}(lambda::T) where {T,SC}
+        if any(lambda .< 0)
+            error("coefficients in λ must be nonnegative")
         else
             new(lambda)
         end
@@ -29,9 +29,9 @@ is_convex(f::Type{<:SqrNormL2}) = true
 is_smooth(f::Type{<:SqrNormL2}) = true
 is_separable(f::Type{<:SqrNormL2}) = true
 is_generalized_quadratic(f::Type{<:SqrNormL2}) = true
-is_strongly_convex(f::Type{<:SqrNormL2}) = true
+is_strongly_convex(f::Type{SqrNormL2{T,SC}}) where {T,SC} = SC
 
-SqrNormL2(lambda::T=1) where T = SqrNormL2{T}(lambda)
+SqrNormL2(lambda::T=1) where T = SqrNormL2{T,all(lambda .> 0)}(lambda)
 
 function (f::SqrNormL2{S})(x) where {S <: Real}
     return f.lambda / real(eltype(x))(2) * norm(x)^2
diff --git a/test/test_calls.jl b/test/test_calls.jl
index dc5b45b..ee24121 100644
--- a/test/test_calls.jl
+++ b/test/test_calls.jl
@@ -442,6 +442,7 @@ test_cases_spec = [
             ( (), randn(Float64, 10) ),
             ( (rand(Float32),), randn(Float32, 10) ),
             ( (rand(Float64),), randn(Float64, 10) ),
+            ( (Float64[1, 1, 1, 1, 0],), randn(Float64, 5) ),
             ( (rand(Float32, 20),), randn(Float32, 20) ),
             ( (rand(Float64, 20),), randn(Float64, 20) ),
             ( (rand(30),), rand(Complex{Float64}, 30) ),