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   "source": [
    "# Interpolation\n",
    "More Information for R interpolation in\n",
    "http://stat.ethz.ch/R-manual/R-patched/library/stats/html/approxfun.html\n",
    "NOTE: this example illustrates an interpolation with random points given from ROOT\n",
    "and procedures made in R's environment.\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Author:** Omar Zapata  \n",
    "<i><small>This notebook tutorial was automatically generated with <a href= \"https://github.com/root-project/root/blob/master/documentation/doxygen/converttonotebook.py\">ROOTBOOK-izer</a> from the macro found in the ROOT repository  on Tuesday, May 19, 2026 at 08:27 PM.</small></i>"
   ]
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   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_44:2:8: error: 'R' is not a class, namespace, or enumeration\n",
      " ROOT::R::TRInterface &r=ROOT::R::TRInterface::Instance();\n",
      "       ^\n",
      "input_line_44:2:8: note: 'R' declared here\n",
      "input_line_44:2:32: error: no member named 'R' in namespace 'ROOT'\n",
      " ROOT::R::TRInterface &r=ROOT::R::TRInterface::Instance();\n",
      "                         ~~~~~~^\n"
     ]
    }
   ],
   "source": [
    "ROOT::R::TRInterface &r=ROOT::R::TRInterface::Instance();"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "362900f0",
   "metadata": {},
   "source": [
    "Creating points"
   ]
  },
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    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_54:2:3: error: use of undeclared identifier 'r'\n",
      " (r[\"x\"] = ((*(std::vector<Double_t>*)0x7f222f444050)))\n",
      "  ^\n",
      "Error in <HandleInterpreterException>: Error evaluating expression (r[\"x\"] = ((*(std::vector<Double_t>*)0x7f222f444050)))\n",
      "Execution of your code was aborted.\n"
     ]
    }
   ],
   "source": [
    "TRandom rg;\n",
    "std::vector<Double_t> x(10),y(10);\n",
    "for(int i=0;i<10;i++)\n",
    "{\n",
    "   x[i]=i;\n",
    "   y[i]=rg.Gaus();\n",
    "}\n",
    "\n",
    "r[\"x\"]=x;\n",
    "r[\"y\"]=y;"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5b37e0fd",
   "metadata": {},
   "source": [
    "do plotting only in non-batch mode"
   ]
  },
  {
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   "execution_count": 3,
   "id": "67ec1999",
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   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "input_line_56:2:3: error: use of undeclared identifier 'r'\n",
      " (r << \"print('Interpolated points')\")\n",
      "  ^\n",
      "Error in <HandleInterpreterException>: Error evaluating expression (r << \"print('Interpolated points')\")\n",
      "Execution of your code was aborted.\n"
     ]
    }
   ],
   "source": [
    "if (!gROOT->IsBatch() )  {\n",
    "\n",
    "   r<<\"dev.new()\";//Required to activate new window for plot\n",
    "   //Plot parameter. Plotting using two rows and one column\n",
    "   r<<\"par(mfrow = c(2,1))\";\n",
    "\n",
    "   //plotting the points\n",
    "   r<<\"plot(x, y, main = 'approx(.) and approxfun(.)')\";\n",
    "\n",
    "   //The function \"approx\" returns a list with components x and y\n",
    "   //containing n coordinates which interpolate the given data points according to the method (and rule) desired.\n",
    "   r<<\"points(approx(x, y), col = 2, pch = '*')\";\n",
    "   r<<\"points(approx(x, y, method = 'constant'), col = 4, pch = '*')\";\n",
    "}\n",
    "else {\n",
    "   r << \"print('Interpolated points')\";\n",
    "   r << \"print(approx(x,y,n=20))\";\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e2b72177",
   "metadata": {},
   "source": [
    "The function \"approxfun\" returns a function performing (linear or constant)\n",
    "interpolation of the given data.\n",
    "For a given set of x values, this function will return the corresponding interpolated values."
   ]
  },
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     "text": [
      "input_line_58:2:3: error: use of undeclared identifier 'r'\n",
      " (r << \"f <- approxfun(x, y)\")\n",
      "  ^\n",
      "Error in <HandleInterpreterException>: Error evaluating expression (r << \"f <- approxfun(x, y)\")\n",
      "Execution of your code was aborted.\n"
     ]
    }
   ],
   "source": [
    "r<<\"f <- approxfun(x, y)\";"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3288c1cd",
   "metadata": {},
   "source": [
    "using approxfun with const method"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "d6c48ab3",
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    "collapsed": false,
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    }
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    {
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     "output_type": "stream",
     "text": [
      "input_line_60:2:3: error: use of undeclared identifier 'r'\n",
      " (r << \"fc <- approxfun(x, y, method = 'const')\")\n",
      "  ^\n",
      "Error in <HandleInterpreterException>: Error evaluating expression (r << \"fc <- approxfun(x, y, method = 'const')\")\n",
      "Execution of your code was aborted.\n"
     ]
    }
   ],
   "source": [
    "r<<\"fc <- approxfun(x, y, method = 'const')\";\n",
    "\n",
    "if (!gROOT->IsBatch() ) {\n",
    "   r<<\"curve(f(x), 0, 11, col = 'green2')\";\n",
    "   r<<\"points(x, y)\";\n",
    "\n",
    "   r<<\"curve(fc(x), 0, 10, col = 'darkblue', add = TRUE)\";\n",
    "   // different interpolation on left and right side :\n",
    "   r<<\"plot(approxfun(x, y, rule = 2:1), 0, 11,col = 'tomato', add = TRUE, lty = 3, lwd = 2)\";\n",
    "}\n",
    "else {\n",
    "   r << \"x2=x+0.5\";\n",
    "   r << \"print('Result of approxfun with default method')\";\n",
    "   r << \"print(paste('x = ',x,'  f(x) = ',f(x2)))\";\n",
    "   r << \"print('Result of approxfun with const method')\";\n",
    "   r << \"print(paste('x = ',x,'  f(x) = ',fc(x2)))\";\n",
    "}"
   ]
  }
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