Logo ROOT  
Reference Guide
Interpolation.C File Reference

Detailed Description

View in nbviewer Open in SWAN More Information for R interpolation in http://stat.ethz.ch/R-manual/R-patched/library/stats/html/approxfun.html NOTE: this example illustrates an interpolation with random points given from ROOT and procedures made in R's environment.

#include<TRInterface.h>
#include<TRandom.h>
#include<vector>
void Interpolation()
{
//Creating points
TRandom rg;
std::vector<Double_t> x(10),y(10);
for(int i=0;i<10;i++)
{
x[i]=i;
y[i]=rg.Gaus();
}
r["x"]=x;
r["y"]=y;
// do plotting only in non-batch mode
if (!gROOT->IsBatch() ) {
r<<"dev.new()";//Required to activate new window for plot
//Plot parameter. Plotting using two rows and one column
r<<"par(mfrow = c(2,1))";
//plotting the points
r<<"plot(x, y, main = 'approx(.) and approxfun(.)')";
//The function "approx" returns a list with components x and y
//containing n coordinates which interpolate the given data points according to the method (and rule) desired.
r<<"points(approx(x, y), col = 2, pch = '*')";
r<<"points(approx(x, y, method = 'constant'), col = 4, pch = '*')";
}
else {
r << "print('Interpolated points')";
r << "print(approx(x,y,n=20))";
}
//The function "approxfun" returns a function performing (linear or constant)
//interpolation of the given data.
//For a given set of x values, this function will return the corresponding interpolated values.
r<<"f <- approxfun(x, y)";
//using approxfun with const method
r<<"fc <- approxfun(x, y, method = 'const')";
if (!gROOT->IsBatch() ) {
r<<"curve(f(x), 0, 11, col = 'green2')";
r<<"points(x, y)";
r<<"curve(fc(x), 0, 10, col = 'darkblue', add = TRUE)";
// different interpolation on left and right side :
r<<"plot(approxfun(x, y, rule = 2:1), 0, 11,col = 'tomato', add = TRUE, lty = 3, lwd = 2)";
}
else {
r << "x2=x+0.5";
r << "print('Result of approxfun with default method')";
r << "print(paste('x = ',x,' f(x) = ',f(x2)))";
r << "print('Result of approxfun with const method')";
r << "print(paste('x = ',x,' f(x) = ',fc(x2)))";
}
}
Author
Omar Zapata

Definition in file Interpolation.C.

TRandom::Gaus
virtual Double_t Gaus(Double_t mean=0, Double_t sigma=1)
Samples a random number from the standard Normal (Gaussian) Distribution with the given mean and sigm...
Definition: TRandom.cxx:263
r
ROOT::R::TRInterface & r
Definition: Object.C:4
ROOT::R::TRInterface
Definition: TRInterface.h:137
TRandom.h
x
Double_t x[n]
Definition: legend1.C:17
TRInterface.h
TRandom
Definition: TRandom.h:27
y
Double_t y[n]
Definition: legend1.C:17
ROOT::R::TRInterface::Instance
static TRInterface & Instance()
static method to get an TRInterface instance reference
Definition: TRInterface.cxx:185
gROOT
#define gROOT
Definition: TROOT.h:406