Initial release

engine/plugins/solvers/dpm2m_ada.lua

@@ -0,0 +1,41 @@
+-- dpm2m_ada.lua: DPM++ 2M Adaptive (step-ratio-corrected AB2)
+-- Adjusts AB2 coefficients based on step size ratio for non-uniform schedules.
+
+solver = {
+    name        = "dpm2m_ada",
+    display     = "DPM++ 2M Adaptive",
+    description = "Step-ratio-corrected AB2 for non-uniform schedules",
+    nfe         = 1,
+    order       = 2,
+    needs_model = false,
+    stateful    = true,
+    stochastic  = false,
+}
+
+local prev_vt = nil
+local prev_dt = 0
+
+function step(xt, vt, t_curr, t_prev, n)
+    if (step_index or 0) == 0 then prev_vt = nil; prev_dt = 0 end
+    local dt = t_curr - t_prev
+
+    if prev_vt and prev_dt > 0 then
+        -- Step-ratio corrected AB2
+        local r  = dt / prev_dt
+        local c1 = 1.0 + r / 2.0
+        local c0 = r / 2.0
+        for i = 0, n - 1 do
+            local v_eff = c1 * vt[i] - c0 * prev_vt[i]
+            xt[i] = xt[i] - v_eff * dt
+        end
+    else
+        -- First step: Euler
+        for i = 0, n - 1 do
+            xt[i] = xt[i] - vt[i] * dt
+        end
+    end
+
+    prev_vt = {}
+    for i = 0, n - 1 do prev_vt[i] = vt[i] end
+    prev_dt = dt
+end