diff --git a/06_iterative.ipynb b/06_iterative.ipynb
index 5dbcb0c..72115d9 100644
--- a/06_iterative.ipynb
+++ b/06_iterative.ipynb
@@ -479,10 +479,10 @@
     "           & &   & 1 & -2\n",
     "    \\end{bmatrix} ~~~ \\text{and} ~~~ \n",
     "    N = \\frac{1}{\\Delta x^2} \\begin{bmatrix}\n",
-    "         0 & 1 & \\\\\n",
-    "          & 0 & 1 \\\\\n",
+    "         0 & -1 & \\\\\n",
+    "          & 0 & -1 \\\\\n",
     "          & & \\ddots & \\ddots \\\\\n",
-    "           & &  & 0 & 1\\\\\n",
+    "           & &  & 0 & -1\\\\\n",
     "           & &   &  & 0\n",
     "    \\end{bmatrix}\n",
     "$$"