Making Lagrange2Tri345 interpolation values exact (#633)

This patche makes shape function evaluation of the Lagrange2Tri345 interpolations exact by reordering some floating point operations. Fixes #582.
Ferrite-FEM · Mar 23, 2023 · ae96dbd · ae96dbd
1 parent cc81e6c
commit ae96dbd
Show file tree

Hide file tree

Showing 2 changed files with 3 additions and 4 deletions.
diff --git a/src/interpolations.jl b/src/interpolations.jl
@@ -552,10 +552,9 @@ function value(ip::Lagrange2Tri345, i::Int, ξ::Vec{2})
     i = permdof2DLagrange2Tri345[order][i]
     ξ_x = ξ[1]
     ξ_y = ξ[2]
-    γ = 1. - ξ_x - ξ_y
     i1, i2, i3 = _numlin_basis2D(i, order)
-    val = one(γ)
-    i1 ≥ 1 && (val *= prod((order * γ - j) / (j + 1) for j = 0:(i1 - 1)))
+    val = one(ξ_y)
+    i1 ≥ 1 && (val *= prod((order - order * (ξ_x + ξ_y ) - j) / (j + 1) for j = 0:(i1 - 1)))
     i2 ≥ 1 && (val *= prod((order * ξ_x - j) / (j + 1) for j = 0:(i2 - 1)))
     i3 ≥ 1 && (val *= prod((order * ξ_y - j) / (j + 1) for j = 0:(i3 - 1)))
     return val

diff --git a/test/test_interpolations.jl b/test/test_interpolations.jl
@@ -9,7 +9,7 @@
                       Lagrange{2, RefTetrahedron, 2}(),
                       Lagrange{2, RefTetrahedron, 3}(),
                       Lagrange{2, RefTetrahedron, 4}(),
-                      #Lagrange{2, RefTetrahedron, 5}(),
+                      Lagrange{2, RefTetrahedron, 5}(),
                       Lagrange{3, RefCube, 1}(),
                       Lagrange{3, RefCube, 2}(),
                       Serendipity{2, RefCube, 2}(),