Using modulo for PeriodicBC

Author: erikvansebille

docs/user_guide/examples/tutorial_nemo.ipynb

@@ -231,18 +231,16 @@
     "    (u1, v1) = fieldset.UV[particles]\n",
     "    x1 = particles.x + u1 * 0.5 * particles.dt\n",
     "    y1 = particles.y + v1 * 0.5 * particles.dt\n",
-    "    x1 = np.where(x1 > 180, x1 - 360, x1)  # keep particles within [-180, 180]\n",
+    "    x1 = ((x1 + 180) % 360) - 180  # keep x1 within [-180, 180]\n",
     "\n",
     "    (u2, v2) = fieldset.UV[\n",
     "        particles.t + 0.5 * particles.dt, particles.z, y1, x1, particles\n",
     "    ]\n",
     "    particles.dx += u2 * particles.dt\n",
     "    particles.dy += v2 * particles.dt\n",
     "\n",
-    "    # update particles.dx to stay within [-180, 180]\n",
-    "    particles.dx = np.where(\n",
-    "        particles.x + particles.dx > 180, particles.dx - 360, particles.dx\n",
-    "    )\n",
+    "    # update particles.dx so particles.x + particles.dx stays within [-180, 180]\n",
+    "    particles.dx = ((particles.x + particles.dx + 180) % 360) - 180 - particles.x\n",
     "\n",
     "\n",
     "pset = parcels.ParticleSet(fieldset, x=lonp, y=latp)\n",