{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Iteration"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now that we have a few examples under our belt, let us take a look at what is happening a bit more closely.\n",
    "\n",
    "As we have identified earlier, TensorFlow allows us to create a graph of operations and variables. These variables are called **Tensors**, and represent data, whether that is a single number, a string, a matrix, or something else. **Tensors** are combined through operations, and this whole process is modelled in a graph.\n",
    "\n",
    "First, make sure you have your **tensorenv** virtual environment activated, Once it is activated type in **conda install jupyter** to install jupter books.\n",
    "\n",
    "Then, run **jupyter notebook** to launch a browser session of the Jupyter Notebook (previously called the IPython Notebook). (If your browser doesn’t open, open it and type **localhost:8888** into the browser’s address bar.)\n",
    "\n",
    "Click “New” and then “Python 3” under “Notebooks”. This will launch a new browser tab. Give the notebook a name by clicking “Untitled” at the top and give it a name (I used “Interactive TensorFlow”).\n",
    "\n",
    "> If you have never used a Jupyter Notebook (or IPython Notebook) before, take a look [at this site](http://opentechschool.github.io/python-data-intro/core/notebook.html) for a brief introduction.\n",
    "\n",
    "Next, as before, let’s create a basic TensorFlow program. One major change is the use of an **InteractiveSession**, which allows us to run variables without needing to constantly refer to the session object (less typing!). Code blocks below are broken into different cells. If you see a break in the code, you will need to run the previous cell first. Also, if you aren’t otherwise confident, ensure all of the code in a given block is type into a cell before you run it."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import tensorflow as tf\n",
    "\n",
    "session = tf.InteractiveSession()\n",
    "\n",
    "x = tf.constant(list(range(10)))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this section of code, we create an **InteractiveSession**, and then define a **constant** value, which is like a placeholder, but with a set value (that doesn’t change). In the next cell, we can evaluate this constant and print the result."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0 1 2 3 4 5 6 7 8 9]\n"
     ]
    }
   ],
   "source": [
    "print(x.eval())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "session.close()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Closing sessions is quite important, and can be easy to forget. For that reason, we were using the **with** keyword in earlier tutorials to handle this. When the **with** block is finished executing, the session will be closed (this also happens if an error happens - the session is still closed).\n",
    "\n",
    "Now lets take a look at a larger example. In this example, we will take a very large matrix and compute on it, keeping track of when memory is used. First, let’s find out how much memory our Python session is currently using:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3944091648 Kb\n"
     ]
    }
   ],
   "source": [
    "import resource\n",
    "print(\"{} Kb\".format(resource.getrusage(resource.RUSAGE_SELF).ru_maxrss))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "On my system, this is using 78496 kilobytes, after running the above code as well. Now, create a new session, and define two matrices:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "session = tf.InteractiveSession()\n",
    "\n",
    "X = tf.constant(np.eye(10000))\n",
    "Y = tf.constant(np.random.randn(10000, 300))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let’s take a look at our memory usage again:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3944091648 Kb\n"
     ]
    }
   ],
   "source": [
    "print(\"{} Kb\".format(resource.getrusage(resource.RUSAGE_SELF).ru_maxrss))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "On my system, the memory usage jumped to 885,220 Kb - those matrices are large!\n",
    "\n",
    "Now, let’s multiply those matrices together using matmul:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "Z = tf.matmul(X, Y)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If we check our memory usage now, we find that no more memory has been used – no actual computation of Z has taken place. It is only when we evaluate the operation do we actually computer this. For an interactive session, you can just use **Z.eval()**, rather than run **session.run(Z)**. Note that you can’t always rely on .eval(), as this is a shortcut that uses the “default” session, not necessarily the one you want to use."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([[-1.34447547,  0.21090638,  0.43680784, ...,  0.73037215,\n",
       "        -0.23213385, -1.12871138],\n",
       "       [ 0.64485571, -0.54936434,  0.35649891, ..., -0.12413736,\n",
       "        -0.58614079, -0.32230335],\n",
       "       [ 0.37195075,  0.20654139, -0.15417305, ...,  0.11346775,\n",
       "         0.23759908, -1.27450529],\n",
       "       ..., \n",
       "       [ 0.63094722, -2.96401008, -1.58592691, ..., -1.57240119,\n",
       "        -0.34051408,  0.53935437],\n",
       "       [-1.97724198, -0.32331035, -0.98294343, ..., -1.56477455,\n",
       "        -0.02398526, -0.37687652],\n",
       "       [-0.70687284,  2.04289277, -0.57564784, ..., -0.40614639,\n",
       "        -0.12381717, -2.23741137]])"
      ]
     },
     "execution_count": 36,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Z.eval()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Your computer will think for quite a while, because only now is it actually performing the action of multiplying those matrices. Checking the memory usage afterwards reveals that this computation has happened, as it now uses nearly 3Gb!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4016365568 Kb\n"
     ]
    }
   ],
   "source": [
    "print(\"{} Kb\".format(resource.getrusage(resource.RUSAGE_SELF).ru_maxrss))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Don’t forget to close your session!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "session.close()"
   ]
  }
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