Restrict domain of square (#9)

Co-authored-by: David Widmann <[email protected]>

Author: oschulz

src/functions.jl

@@ -1,8 +1,12 @@
 # This file is a part of InverseFunctions.jl, licensed under the MIT License (MIT).
 
 """
-    square(x)
+    square(x::Real)
 
 Inverse of `sqrt(x)` for non-negative `x`.
 """
 square(x) = x^2
+function square(x::Real)
+    x < zero(x) && throw(DomainError(x, "`square` is defined as the inverse of `sqrt` and can only be evaluated for non-negative values"))
+    return x^2
+end

test/test_functions.jl

@@ -5,7 +5,9 @@ using InverseFunctions
 
 
 @testset "square" begin
-    for x in (-0.72, 0.73, randn(3, 3))
+    for x in (0.0, 0.73)
         @test InverseFunctions.square(x) ≈ x * x
     end
+
+    @test_throws DomainError InverseFunctions.square(-1)
 end