surface pressure load tet4 + test

src/postprocess_utils.jl

@@ -0,0 +1,33 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+"""
+Calculate field values to nodal points from Gauss points using least-squares fitting.
+"""
+function calc_nodal_values!(elements, field_name, field_dim, time)
+    A = SparseMatrixCOO()
+    b = SparseMatrixCOO()
+    for element in elements
+        gdofs = get_connectivity(element)
+        for ip in get_integration_points(element)
+            detJ = element(ip, time, Val{:detJ})
+            w = ip.weight*detJ
+            f = ip(field_name, time)
+            N = element(ip, time)
+            add!(A, gdofs, gdofs, w*kron(N', N))
+            for dim=1:field_dim
+                add!(b, gdofs, w*f[dim]*N, dim)
+            end
+        end
+    end
+    A = sparse(A)
+    b = sparse(b)
+    nz = get_nonzero_rows(A)
+    x = zeros(size(b)...)
+    x[nz, :] = A[nz,nz] \ b[nz, :]
+    nodal_values = Dict()
+    for i=1:size(x,1)
+        nodal_values[i] = vec(x[i,:])
+    end
+    update!(elements, field_name, nodal_values)
+end