Truncate polynomial if it has zeros in the trailing elements (#12)

Truncate polynomial if it has zeros in the trailing elements

src/PolynomialRoots.jl

@@ -609,8 +609,15 @@ end
 
 function roots(poly::AbstractVector{N}; epsilon::AbstractFloat=NaN,
                polish::Bool=false) where {N<:Number}
-    degree = length(poly) - 1
-    roots!(zeros(Complex{real(float(N))}, degree), float.(complex(poly)),
+    # Before starting, truncate the polynomial if it has zeros in the trailing elements
+    last_nz = findlast(!iszero, poly)
+    if lastindex(poly) == last_nz
+        _poly = poly
+    else
+        _poly = poly[1:last_nz]
+    end
+    degree = length(_poly) - 1
+    roots!(zeros(Complex{real(float(N))}, degree), float.(complex(_poly)),
            epsilon, degree, polish)
 end
 

test/runtests.jl

@@ -228,6 +228,9 @@ end
             -47.40236121905153, -71.92379520244637, -57.977452001749555]
     @test isapprox(zeros(length(poly)-1),
                    evalpoly(@inferred(roots(poly)), poly), atol = 2e-11)
+    # https://github.com/giordano/PolynomialRoots.jl/issues/11
+    poly = [1.0, -2.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0]
+    @test isapprox(@inferred(roots(poly)), [1, 1])
 end
 
 @testset "Errors" begin