Update Chapter 04 - Expectation.ipynb

missing two minus signs for the covariance matrix of the multinomial distribution.

Author: ang-gr

Chapter 04 - Expectation.ipynb

@@ -278,8 +278,8 @@
     "\\mathbb{E}(X) = np = n(p_1, \\dots, p_k)\n",
     "\\quad \\text{and} \\quad\n",
     "\\mathbb{V}(X) = \\begin{pmatrix}\n",
-    "np_1(1 - p_1) & -np_1p_2 & \\cdots & np_1p_k \\\\\n",
-    "-np_2p_1 & np_2(1 - p_2) & \\cdots & np_2p_k \\\\\n",
+    "np_1(1 - p_1) & -np_1p_2 & \\cdots & -np_1p_k \\\\\n",
+    "-np_2p_1 & np_2(1 - p_2) & \\cdots & -np_2p_k \\\\\n",
     "\\vdots & \\vdots & \\ddots & \\vdots \\\\\n",
     "-np_kp_1 & -np_kp_2 & \\cdots & np_k(1 - p_k)\n",
     "\\end{pmatrix} $$\n",