grasp_np.meshgrid.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## np.meshgrid"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Return coordinate matrices from coordinate vectors.\n",
    "\n",
    "Make N-D coordinate arrays for vectorized evaluations of N-D scalar/vector fields over N-D grids, given one-dimensional coordinate arrays x1, x2,..., xn."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.646184Z",
     "start_time": "2018-06-11T07:56:31.378845Z"
    }
   },
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import matplotlib.pyplot as plt"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.654164Z",
     "start_time": "2018-06-11T07:56:31.648181Z"
    }
   },
   "outputs": [],
   "source": [
    "x = [1, 2, 3]\n",
    "y = [4, 5, 6, 7]\n",
    "xx, yy = np.meshgrid(x, y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "xx: ${len(y)} \\times {len(x)}$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.665133Z",
     "start_time": "2018-06-11T07:56:31.657165Z"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[1, 2, 3],\n",
       "       [1, 2, 3],\n",
       "       [1, 2, 3],\n",
       "       [1, 2, 3]])"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "xx"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.674110Z",
     "start_time": "2018-06-11T07:56:31.667138Z"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3])"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "xx.ravel()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:46:07.028063Z",
     "start_time": "2018-06-11T07:46:07.022076Z"
    }
   },
   "source": [
    "yy: ${len(y)} \\times {len(x)}$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.683085Z",
     "start_time": "2018-06-11T07:56:31.677102Z"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[4, 4, 4],\n",
       "       [5, 5, 5],\n",
       "       [6, 6, 6],\n",
       "       [7, 7, 7]])"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "yy"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.692065Z",
     "start_time": "2018-06-11T07:56:31.686077Z"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7])"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "yy.ravel()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.701037Z",
     "start_time": "2018-06-11T07:56:31.695053Z"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[1, 4],\n",
       "       [2, 4],\n",
       "       [3, 4],\n",
       "       [1, 5],\n",
       "       [2, 5],\n",
       "       [3, 5],\n",
       "       [1, 6],\n",
       "       [2, 6],\n",
       "       [3, 6],\n",
       "       [1, 7],\n",
       "       [2, 7],\n",
       "       [3, 7]])"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Z = np.c_[xx.ravel(), yy.ravel()]\n",
    "Z"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "ExecuteTime": {
     "end_time": "2018-06-11T07:56:31.817743Z",
     "start_time": "2018-06-11T07:56:31.704028Z"
    }
   },
   "outputs": [
    {
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      "text/plain": [
       "<Figure size 432x288 with 1 Axes>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "plt.plot(Z[:, 0], Z[:, 1], \"ro\")\n",
    "plt.xticks([1., 2., 3.])\n",
    "plt.yticks([4., 5., 6., 7.])\n",
    "plt.grid(True)"
   ]
  }
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