all tests pass now

src/elements_nurbs.jl

@@ -1,6 +1,9 @@
 # This file is a part of JuliaFEM.
 # License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
 
+using ForwardDiff
+# TODO: evaluate partial derivatives of basis functions without forwarddiff
+
 """ NURBS segment. """
 type NSeg <: AbstractElement
     order :: Int
@@ -98,6 +101,14 @@ function get_basis(element::Element{NSolid}, xi::Vector, time)
     return N / sum(N)
 end
 
+# TODO: evaluate partial derivatives of basis functions without forwarddiff
+""" Evaluate partial derivatives of basis functions using ForwardDiff. """
+function get_dbasis{E<:Union{NSeg, NSurf, NSolid}}(element::Element{E}, ip, time)
+    xi = isa(ip, IP) ? ip.coords : ip
+    basis(xi) = vec(get_basis(element, xi, time))
+    return ForwardDiff.jacobian(basis, xi)'
+end
+
 function length(element::Element{NSeg})
     nu = length(element.properties.knots) - element.properties.order - 1
     return nu