Tutorial-Indexed_Expressions_soln.ipynb

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    "\n",
    "# The NRPy+ code required to generate the needed C code for the lowering operator: $g_{ij} \\beta^i$, with the result set to C variables \"`betaD0out`\", \"`betaD1out`\", and \"`betaD2out`\" \n",
    "\n",
    "## *Courtesy Zach Etienne*"
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      "/*\n",
      " *  Original SymPy expressions:\n",
      " *  \"[betaD0out = betaU0*hDD00 + betaU1*hDD01 + betaU2*hDD02,\n",
      " *    betaD1out = betaU0*hDD01 + betaU1*hDD11 + betaU2*hDD12,\n",
      " *    betaD2out = betaU0*hDD02 + betaU1*hDD12 + betaU2*hDD22]\"\n",
      " */\n",
      "{\n",
      "   betaD0out = betaU0*hDD00 + betaU1*hDD01 + betaU2*hDD02;\n",
      "   betaD1out = betaU0*hDD01 + betaU1*hDD11 + betaU2*hDD12;\n",
      "   betaD2out = betaU0*hDD02 + betaU1*hDD12 + betaU2*hDD22;\n",
      "}\n",
      "\n"
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   "source": [
    "# The NRPy_param_funcs module sets up global structures that manage free parameters within NRPy+\n",
    "import NRPy_param_funcs as par   # NRPy+: Parameter interface\n",
    "# The indexedexp module defines various functions for defining and managing indexed quantities like tensors and pseudotensors\n",
    "import indexedexp as ixp         # NRPy+: Symbolic indexed expression (e.g., tensors, vectors, etc.) support\n",
    "# The grid module defines various parameters related to a numerical grid or the dimensionality of indexed expressions\n",
    "# For example, it declares the parameter DIM, which specifies the dimensionality of the indexed expression\n",
    "import grid as gri               # NRPy+: Functions having to do with numerical grids\n",
    "from outputC import outputC      # NRPy+: Basic C code output functionality\n",
    "\n",
    "# Set the dimension to 3\n",
    "par.set_parval_from_str(\"DIM\",3)\n",
    "\n",
    "# Declare rank-1 contravariant (\"U\" and \"D\") vectors\n",
    "betaU = ixp.declarerank1(\"betaU\")\n",
    "betaD = ixp.zerorank1()\n",
    "\n",
    "# Declare h_{ij}=hDD[i][j] and h^{ij}=hUU[i][j]\n",
    "hDD = ixp.declarerank2(\"hDD\",\"sym01\")\n",
    "\n",
    "# Get the dimension we just set (should be set to 3).\n",
    "DIM = par.parval_from_str(\"DIM\")\n",
    "\n",
    "for i in range(DIM):\n",
    "    for j in range(DIM):\n",
    "        betaD[j] += betaU[i]*hDD[i][j]\n",
    "\n",
    "outputC(betaD,[\"betaD0out\",\"betaD1out\",\"betaD2out\"])"
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