Fix time interpolation (#23)

JuliaFEM · May 25, 2018 · 1b4027f · 1b4027f
1 parent f77832e
commit 1b4027f
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Showing 2 changed files with 26 additions and 4 deletions.
diff --git a/src/fields.jl b/src/fields.jl
@@ -132,8 +132,9 @@ function interpolate_field(field::DCTV, time)
         if t0 < time < t1
             y0 = field.data[i-1].second
             y1 = field.data[i].second
-            f = (time-t0)/(t1-t0)
-            return f*y0 + (1-f)*y1
+            dy = y1-y0
+            dt = t1-t0
+            return y0 + (time-t0)*dy/dt
         end
     end
 end
@@ -179,8 +180,8 @@ function interpolate_field{N,T}(field::DVTV{N,T}, time)
         if t0 < time < t1
             y0 = field.data[i-1].second
             y1 = field.data[i].second
-            f = (time-t0)/(t1-t0)
-            return map((a,b) -> f*a + (1-f)*b, y0, y1)
+            dt = t1-t0
+            return map((a,b) -> a + (time-t0)*(b-a)/dt, y0, y1)
         end
     end
 end

diff --git a/test/test_time_interpolate.jl b/test/test_time_interpolate.jl
@@ -0,0 +1,21 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/FEMBase.jl/blob/master/LICENSE
+
+using FEMBase
+using FEMBase.Test
+
+# Time interpolation of fields
+
+element = Element(Seg2, [1, 2])
+update!(element, "force", 1.0 => 15.0)
+update!(element, "force", 2.0 => 30.0)
+@test isapprox(element("force", 1.0), 15.0)
+@test isapprox(element("force", 1.2), 18.0)
+@test isapprox(element("force", 1.6), 24.0)
+@test isapprox(element("force", 2.0), 30.0)
+
+update!(element, "temperature", 0.0 => (1.0, 3.0))
+update!(element, "temperature", 1.0 => (2.0, 14.0))
+@test isapprox(element("temperature", (0.0,), 0.0), 2.0)
+@test isapprox(element("temperature", (0.0,), 0.3), 3.8)
+@test isapprox(element("temperature", (0.0,), 1.0), 8.0)