p29_1_broadcast.ipynb

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    "import numpy as np"
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    {
     "data": {
      "text/plain": "array([[9, 4],\n       [9, 5],\n       [1, 7]])"
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     "execution_count": 2,
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    "a = np.random.randint(1, 10, [3, 2])\n",
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     "data": {
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     "execution_count": 3,
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    "b = np.random.randint(1, 10, [2])\n",
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   "cell_type": "code",
   "execution_count": 5,
   "outputs": [
    {
     "data": {
      "text/plain": "array([[14, 11],\n       [14, 12],\n       [ 6, 14]])"
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     "execution_count": 5,
     "metadata": {},
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    "a + b"
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   "source": [
    "# 可广播条件\n",
    "# 1. 两个矩阵形状相等\n",
    "# 2. 如果A和B的形状有一个不相等且维度是1，其他维度都相等，比如[3,5,7]和[3,1,7]的第二个维度不相等\n",
    "#    但是这个维度有一个是1，所以依旧可以进行广播；若两个维度不相等，且不相等的也为1，仍然\n",
    "#    可以进行广播；\n",
    "# 3. 如果若A和B满足可广播性，则在A或者B的头部加上任意一个维度，新矩阵仍然和原先的矩阵满足\n",
    "#    广播性，比如[2,3,1,7]和[3,5,7]是匹配的"
   ],
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     "name": "#%%\n"
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  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "source": [
    "a = np.array([9, 2, 3, 12])\n",
    "b = np.array([9, 2, 3, 2, 6])\n",
    "# 此时a和b不匹配，不能广播"
   ],
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