Add convert(Matrix{T},Bidigonal{S}) method. Fixes #12729.

base/linalg/bidiag.jl

@@ -42,7 +42,20 @@ end
 
 #Converting from Bidiagonal to dense Matrix
 full{T}(M::Bidiagonal{T}) = convert(Matrix{T}, M)
-convert{T}(::Type{Matrix{T}}, A::Bidiagonal{T})=diagm(A.dv) + diagm(A.ev, A.isupper?1:-1)
+function convert{T}(::Type{Matrix{T}}, A::Bidiagonal)
+    n = size(A, 1)
+    B = zeros(T, n, n)
+    for i = 1:n - 1
+        B[i,i] = A.dv[i]
+        if A.isupper
+            B[i, i + 1] = A.ev[i]
+        else
+            B[i + 1, i] = A.ev[i]
+        end
+    end
+    B[n,n] = A.dv[n]
+    return B
+end
 convert{T}(::Type{Matrix}, A::Bidiagonal{T}) = convert(Matrix{T}, A)
 promote_rule{T,S}(::Type{Matrix{T}}, ::Type{Bidiagonal{S}})=Matrix{promote_type(T,S)}
 

test/linalg/bidiag.jl

@@ -160,6 +160,9 @@ for relty in (Float32, Float64, BigFloat), elty in (relty, Complex{relty})
         debug && println("Inverse")
         @test_approx_eq inv(T)*Tfull eye(elty,n)
     end
+
+    @test Matrix{Complex{Float64}}(BD) == BD
+
 end
 
 # Issue 10742 and similar