diff --git a/src/arrays/arraymath.jl b/src/arrays/arraymath.jl
index f73fb3e..3c13415 100644
--- a/src/arrays/arraymath.jl
+++ b/src/arrays/arraymath.jl
@@ -121,6 +121,11 @@ function \{B<:OrthonormalBasis}(op::AbstractQuMatrix{B}, vec::AbstractQuVector{B
     return QAT(div, bases(op,1))
 end
 
+# convert coeffs to complex
+Base.complex{B<:OrthonormalBasis}(qarr::AbstractQuArray{B}) = similar_type(qarr)(complex(coeffs(qarr)), bases(qarr))
+Base.float{B<:OrthonormalBasis}(qarr::AbstractQuArray{B}) = similar_type(qarr)(float(coeffs(qarr)), bases(qarr))
+Base.int{B<:OrthonormalBasis}(qarr::AbstractQuArray{B}) = similar_type(qarr)(int(coeffs(qarr)), bases(qarr))
+
 #  Vectorize QuArray
 Base.vec{B<:OrthonormalBasis}(vec1::AbstractQuArray{B}) = QuArray(vec(coeffs(vec1)))
 
@@ -198,8 +203,15 @@ tensor(bra::DualVector, ket::AbstractQuVector) = tensor(ket, bra)
 commute(a::AbstractQuMatrix, b::AbstractQuMatrix) = (a*b) - (b*a)
 anticommute(a::AbstractQuMatrix, b::AbstractQuMatrix) = (a*b) + (b*a)
 
+###############
+#  Expectaion #
+###############
+expectation(qarr::AbstractQuVector, op::AbstractQuMatrix) = vec(qarr)'*op*vec(qarr)
+expectation(qarr::AbstractQuMatrix, op::AbstractQuMatrix) = trace(qarr*op)
+
 export normalize,
     normalize!,
     tensor,
     commute,
-    anticommute
+    anticommute,
+    expectation
diff --git a/test/multest.jl b/test/multest.jl
index fb93748..056cfa6 100644
--- a/test/multest.jl
+++ b/test/multest.jl
@@ -55,3 +55,8 @@ qv1 = normalize!(QuArray(v1))
 
 # Vectorize
 @assert vec(qv) == vec(qv')
+
+# Complex coeffs
+@assert complex(statevec(1, FiniteBasis(2))) == QuArray([1.+0.*im, 0.+0.*im])
+@assert float(statevec(1, FiniteBasis(2))) == QuArray([1., 0.])
+@assert int(statevec(1, FiniteBasis(2))) == QuArray([1, 0])