Add new method to set properties for problem

```
update!(body.properties, "a" => "b", "c" => "d")
```

Usage example is shown in
`test_elasticity_2d_linear_with_surface_load.jl`.

src/problems.jl

@@ -141,6 +141,24 @@ function get_assembly(problem)
     return problem.assembly
 end
 
+"""
+    update!(problem.properties, attr...)
+
+Update properties for a problem.
+
+# Example
+
+```julia
+update!(body.properties, "finite_strain" => "false")
+```
+"""
+function update!{P<:AbstractProblem}(problem::P, attr::Pair{String, String}...)
+    for (name, value) in attr
+        debug("$P: set $name to $value")
+        setfield!(problem, parse(name), parse(value))
+    end
+end
+
 """ Initialize element ready for calculation. """
 function initialize!(problem::Problem, element::Element, time::Float64)
     field_name = get_unknown_field_name(problem)

test/test_elasticity_2d_linear_with_surface_load.jl

@@ -1,52 +1,46 @@
 # This file is a part of JuliaFEM.
 # License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
 
+using Base.Test
 using JuliaFEM
-using JuliaFEM.Preprocess
-using JuliaFEM.Postprocess
-using JuliaFEM.Testing
 
-#=
-- solve 2d plane stress problem with known solution:
-    surface traction force in 2d
-    volume load in 2d
-=#
-@testset "test 2d linear elasticity with surface + volume load" begin
-    meshfile = "/geometry/2d_block/BLOCK_1elem.med"
-    mesh = aster_read_mesh(dirname(@__DIR__)*meshfile)
+@testset "2d linear elasticity + volume load + surface load" begin
+
+    X = Dict(1 => [0.0, 0.0],
+             2 => [1.0, 0.0],
+             3 => [1.0, 1.0],
+             4 => [0.0, 1.0])
+
+    props = ("formulation" => "plane_stress",
+             "finite_strain" => "false",
+             "geometric_stiffness" => "false")
 
     # field problem
     block = Problem(Elasticity, "BLOCK", 2)
-    block.properties.formulation = :plane_stress
-    block.properties.finite_strain = false
-    block.properties.geometric_stiffness = false
-    block.elements = create_elements(mesh, "BLOCK")
+    block.elements = [Element(Quad4, [1, 2, 3, 4])]
+    update!(block.properties, props...)
+    update!(block.elements, "geometry", X)
     update!(block.elements, "youngs modulus", 288.0)
     update!(block.elements, "poissons ratio", 1/3)
     update!(block.elements, "displacement load 2", 576.0)
 
     # traction
     traction = Problem(Elasticity, "TRACTION", 2)
-    traction.properties.formulation = :plane_stress
-    traction.properties.finite_strain = false
-    traction.properties.geometric_stiffness = false
-    traction.elements = create_elements(mesh, "TOP")
-    update!(traction, "displacement traction force 2", 288.0)
+    traction.elements = [Element(Seg2, [3, 4])]
+    update!(traction.properties, props...)
+    update!(traction.elements, "geometry", X)
+    update!(traction.elements, "displacement traction force 2", 288.0)
 
     # boundary conditions
-    bc_sym_23 = Problem(Dirichlet, "symmetry bc 23", 2, "displacement")
-    bc_sym_23.elements = create_elements(mesh, "LEFT")
-    update!(bc_sym_23, "displacement 1", 0.0)
-    bc_sym_13 = Problem(Dirichlet, "symmetry bc 13", 2, "displacement")
-    bc_sym_13.elements = create_elements(mesh, "BOTTOM")
-    update!(bc_sym_13, "displacement 2", 0.0)
+    bc = Problem(Dirichlet, "symmetry boundary conditions", 2, "displacement")
+    bc.elements = [Element(Seg2, [1, 2]), Element(Seg2, [4, 1])]
+    update!(bc.elements, "geometry", X)
+    update!(bc.elements[1], "displacement 2", 0.0)
+    update!(bc.elements[2], "displacement 1", 0.0)
 
-    solver = Solver(Linear, block, traction, bc_sym_23, bc_sym_13)
+    solver = Solver(Linear, block, traction, bc)
     solver()
 
-    info("u = ", block.assembly.u)
-    info("λ = ", block.assembly.la)
-
     f = 288.0
     g = 576.0
     E = 288.0