added description how to formulate new problems

src/problems.jl

@@ -0,0 +1,52 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+abstract Problem
+
+get_equations(pr::Problem) = pr.equations
+get_dimension(pr::Type{Problem}) = nothing
+get_equation(pr::Type{Problem}, el::Type{Element}) = nothing
+
+"""
+Add new element to problem
+"""
+function add_element!(pr::Problem, el::Element)
+    eq = get_equation(typeof(pr), typeof(el))
+    push!(pr.equations, eq(el))
+end
+
+"""
+Return total number of basis functions in problem
+"""
+function get_number_of_basis_functions(pr::Problem)
+    conn = Int[]
+    for eq in get_equations(pr)
+        append!(conn, get_connectivity(eq))
+    end
+    length(unique(conn))
+end
+
+"""
+Problem matrix size dimension
+"""
+function get_matrix_dimension(pr::Problem)
+    get_dimension(typeof(pr))*get_number_of_basis_functions(pr)
+end
+
+"""
+Assign global dofs for element. This doesn't do any reordering.
+"""
+function set_global_dofs!(pr::Problem)
+    #ndim = get_dimension(pr)*get_number_of_basis_functions(pr)
+    #ndim = get_matrix_dimension(pr)
+    dim = get_dimension(typeof(pr))
+    nconn = get_number_of_basis_functions(pr)
+    ndim = dim*nconn
+    Logging.debug("Problem (matrix) dimension: $ndim")
+    gdofs = reshape(collect(1:ndim), dim, nconn)
+    for eq in get_equations(pr)
+        lconn = get_connectivity(eq)
+        gconn = gdofs[:, lconn][:]
+        set_global_dofs!(eq, gconn)
+    end
+end