Got rid of pylab.hold (depracated)

Author: mathemusician

ipython/CoupledSpringMassSystem.ipynb

@@ -191,7 +191,7 @@
       "figure(1, figsize=(6, 4.5))\n",
       "\n",
       "xlabel('t')\n",
-      "hold(True)\n",
+      "grid(True)\n",
       "lw = 1\n",
       "\n",
       "plot(t, x1, 'b', linewidth=lw)\n",