Initial release

engine/plugins/schedulers/ddim_uniform.lua

@@ -0,0 +1,37 @@
+-- ddim_uniform.lua: DDIM Uniform — log-SNR uniform (S-shaped)
+
+scheduler = {
+    name        = "ddim_uniform",
+    display     = "DDIM Uniform",
+    description = "Log-SNR uniform (S-shaped)",
+}
+
+function schedule(output, num_steps, shift)
+    local t_max = 0.9986
+    local t_min = 0.0014
+    local logit_max = math.log(t_max / (1 - t_max))
+    local logit_min = math.log(t_min / (1 - t_min))
+
+    for i = 0, num_steps - 1 do
+        local frac = i / num_steps
+        local logit_t = logit_max + (logit_min - logit_max) * frac
+        output[i] = 1.0 / (1.0 + math.exp(-logit_t))
+    end
+    clamp(output, num_steps)
+    apply_shift(output, num_steps, shift)
+end
+
+function apply_shift(ts, n, shift)
+    if shift == 1.0 then return end
+    for i = 0, n - 1 do
+        local t = ts[i]
+        ts[i] = shift * t / (1.0 + (shift - 1.0) * t)
+    end
+end
+
+function clamp(ts, n)
+    for i = 0, n - 1 do
+        if ts[i] < 1e-6 then ts[i] = 1e-6 end
+        if ts[i] > 1.0 then ts[i] = 1.0 end
+    end
+end