rtx-cfd embedded3 item 1: the Poisson core as poisson/{problem, hierarchy, pcg} (≤ 385 lines each; the periodic wrap built once into neighbour arrays); gate 1 HELD: nz=1 bit-identical to the 2D solver (lex + red-black, cached/uncached, iterations) and every extrusion case bit-identical to the three_d oracle, planes within 1.4e-11

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/grid.rs

@@ -0,0 +1,83 @@
+//! The uniform Cartesian grid and its index conventions.
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct Grid {
+    pub nx: usize,
+    pub ny: usize,
+    pub nz: usize,
+    pub dx: f64,
+    pub dy: f64,
+    pub dz: f64,
+}
+
+impl Grid {
+    /// Cubic cells of spacing `h`.
+    #[must_use]
+    pub fn cubic(nx: usize, ny: usize, nz: usize, h: f64) -> Self {
+        Self {
+            nx,
+            ny,
+            nz,
+            dx: h,
+            dy: h,
+            dz: h,
+        }
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn cells(&self) -> usize {
+        self.nx * self.ny * self.nz
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn cell(&self, k: usize, j: usize, i: usize) -> usize {
+        (k * self.ny + j) * self.nx + i
+    }
+
+    /// `(k, j, i)` of a cell index.
+    #[inline]
+    #[must_use]
+    pub fn kji(&self, idx: usize) -> (usize, usize, usize) {
+        let nxy = self.nx * self.ny;
+        (idx / nxy, (idx % nxy) / self.nx, idx % self.nx)
+    }
+
+    /// The u face west of cell `(k, j, i)`; `i = nx` is the east face of the last cell.
+    #[inline]
+    #[must_use]
+    pub fn uface(&self, k: usize, j: usize, i: usize) -> usize {
+        (k * self.ny + j) * (self.nx + 1) + i
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn vface(&self, k: usize, j: usize, i: usize) -> usize {
+        (k * (self.ny + 1) + j) * self.nx + i
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn wface(&self, k: usize, j: usize, i: usize) -> usize {
+        (k * self.ny + j) * self.nx + i
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn n_ufaces(&self) -> usize {
+        (self.nx + 1) * self.ny * self.nz
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn n_vfaces(&self) -> usize {
+        self.nx * (self.ny + 1) * self.nz
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn n_wfaces(&self) -> usize {
+        self.nx * self.ny * (self.nz + 1)
+    }
+}