clarifying why cic_paint_dx is slower

notebooks/01-Introduction.ipynb

@@ -244,6 +244,12 @@
    "id": "02f18b52",
    "metadata": {},
    "source": [
+    "We note that **painting only displacements is slower** than painting absolute particle positions.\n",
+    "\n",
+    "This slower performance occurs because **painting displacements requires processing in smaller chunks or batches**. Instead of creating a large array of particle positions with neighbors (e.g., `(NParticles, 3, 8)`), which consumes a significant amount of memory, we paint the particles in manageable batches.\n",
+    "\n",
+    "This trade-off allows for greater memory efficiency but comes at the expense of speed. By reducing the memory footprint, we avoid memory limitations, especially useful in large-scale or distributed PM simulations, even if it means slightly slower painting.\n",
+    "\n",
     "We’ll see in later notebooks that retaining only the displacement is essential for distributed Particle Mesh (PM) simulations, where memory efficiency and computational speed are key.\n"
    ]
   }