{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Tutorial 02: Deriving a dynamics term\n",
    "\n",
    "> Interactive online tutorial:\n",
    "> [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/ubermag/micromagneticmodel/master?filepath=docs%2Fipynb%2Findex.ipynb)\n",
    "\n",
    "All dynamics terms in `micromagneticmodel` are in `micromagneticmodel/dynamics` directory. They are all derived from `micromagneticmodel.dynamics.DynamicsTerm` base class.\n",
    "\n",
    "For instance, let us say we want to implement a dynamics term with following specifications:\n",
    "\n",
    "| property | value |\n",
    "| --- | --- |\n",
    "| name | `SpecialDynamics` |\n",
    "| expression | $\\xi\\mathbf{m}\\times\\mathbf{v}$ |\n",
    "| parameters | $\\xi$, $\\mathbf{v}$ |\n",
    "| parameter properties | $\\xi \\ge 0$, can be spatially varying |\n",
    "|  | $\\mathbf{v}$ is three-dimensional, can be spatially varying |\n",
    "\n",
    "The dynamics term class would be:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import micromagneticmodel as mm\n",
    "\n",
    "class SpecialDynamics(mm.DynamicsTerm):\n",
    "    def __init__(self, xi, v, name='specialdynamics'):\n",
    "        self.xi = xi\n",
    "        self.v = v\n",
    "        self.name = name"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now, we can try to instantiate it"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Exception raised.\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    sd = SpecialDynamics(xi=0.1, v=(0, 0, 1))\n",
    "except TypeError:\n",
    "    print('Exception raised.')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "An exception was raised because `_repr` and `_latex` properties must be implemented. Therefore, an extended implementation of the class is:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "class SpecialDynamics(mm.DynamicsTerm):\n",
    "    _latex = r'$\\xi\\mathbf{m}\\times\\mathbf{v}$'\n",
    "\n",
    "    def __init__(self, xi, v, name='specialdynamics'):\n",
    "        self.xi = xi\n",
    "        self.v = v\n",
    "        self.name = name\n",
    "\n",
    "    @property\n",
    "    def _repr(self):\n",
    "        return f'SpecialDynamics(xi={self.xi}, v={self.v}, name=\\'{self.name}\\')'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can try to instantiate the class again:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/latex": [
       "$\\xi\\mathbf{m}\\times\\mathbf{v}$"
      ],
      "text/plain": [
       "SpecialDynamics(xi=0.1, v=(0, 0, 1), name='specialdynamics')"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sd = SpecialDynamics(xi=0.1, v=(0, 0, 1))\n",
    "sd"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The dynamics object is created. The last thing we have to impose on the energy class is the typesystem. More precisely, we have to make sure no negative $\\xi$ values are allowed, $\\mathbf{v}$ is three-dimensional and that `name` attribute accepts only valid Python variable names. This is done by using `ubermagutil`. Full documentation can be found [here](https://ubermagutil.readthedocs.io/en/latest/)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "import ubermagutil.typesystem as ts\n",
    "import discretisedfield as df\n",
    "\n",
    "\n",
    "@ts.typesystem(xi=ts.Parameter(descriptor=ts.Scalar(unsigned=True), otherwise=df.Field),\n",
    "               v=ts.Parameter(descriptor=ts.Vector(size=3), otherwise=df.Field),\n",
    "               name=ts.Name())\n",
    "class SpecialDynamics(mm.DynamicsTerm):\n",
    "    _latex = r'$\\xi\\mathbf{m}\\times\\mathbf{v}$'\n",
    "\n",
    "    def __init__(self, xi, v, name='specialdynamics'):\n",
    "        self.xi = xi\n",
    "        self.v = v\n",
    "        self.name = name\n",
    "\n",
    "    @property\n",
    "    def _repr(self):\n",
    "        return f'SpecialDynamics(xi={self.xi}, v={self.v}, name=\\'{self.name}\\')'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "If we now attempt to pass invalid input arguments, exceptions are raised."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Exception raised.\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    sd = SpecialDynamics(xi=-0.1, v=(0, 0, 1))  # negative xi\n",
    "except ValueError:\n",
    "    print('Exception raised.')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Exception raised.\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    sd = SpecialDynamics(xi=0.1, v=(0, 1))  # 2D v\n",
    "except ValueError:\n",
    "    print('Exception raised.')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Some of the properties and methods of the implemented energy term are:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "sd = SpecialDynamics(xi=0.1, v=(0, 1, 1), name='specialdynamics')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0.1"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sd.xi"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(0, 1, 1)"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sd.v"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'specialdynamics'"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sd.name"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/latex": [
       "$\\xi\\mathbf{m}\\times\\mathbf{v}$"
      ],
      "text/plain": [
       "SpecialDynamics(xi=0.1, v=(0, 1, 1), name='specialdynamics')"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "sd"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\"SpecialDynamics(xi=0.1, v=(0, 1, 1), name='specialdynamics')\""
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "repr(sd)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Finally, the class we have just implemented is going to be inherited by a specific micromagnetic calculator, where `_script` method is going to be implemented."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Exception raised.\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    sd._script\n",
    "except NotImplementedError:\n",
    "    print('Exception raised.')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Other\n",
    "\n",
    "Full description of all existing descriptors can be found in the [API Reference](https://micromagneticmodel.readthedocs.io/en/latest/?badge=latest)."
   ]
  }
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