Add sample_package with linear algebra tools

- add sample_package:
  + __init__.py => high-level description and imports
  + matrix.py => define a Matrix class
  + vector.py => define a Vector class
  + utils.py => package-wide utilities
- streamline the code snippets in the chapter 11 notebooks
  to align with the sample_package

11_classes/02_content.ipynb

@@ -1815,17 +1815,16 @@
    },
    "outputs": [],
    "source": [
-    "def norm(vector_or_matrix):\n",
+    "def norm(vec_or_mat):\n",
     "    \"\"\"Calculate the Frobenius or Euclidean norm of a matrix or vector.\n",
     "\n",
     "    Args:\n",
-    "        vector_or_matrix (Vector/Matrix): the entries whose squares\n",
-    "            are summed up\n",
+    "        vec_or_mat (Vector / Matrix): object whose entries are squared and summed up\n",
     "\n",
     "    Returns:\n",
     "        norm (float)\n",
     "    \"\"\"\n",
-    "    return math.sqrt(sum(x ** 2 for x in vector_or_matrix))"
+    "    return math.sqrt(sum(x ** 2 for x in vec_or_mat))"
    ]
   },
   {