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@hamaluik
Created January 15, 2013 04:53
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Basic linear interpolator class in C++
#include <map>
#include <vector>
/**
* Provides a basic interpolation mechanism in C++ using the STL.
* Maybe not the fastest or most elegant method, but it works (for
* linear interpolation!!), and is fast enough for a great deal of
* purposes. It's also super easy to use, so that's a bonus.
*/
class LinearInterpolator {
public:
LinearInterpolator() {}
/**
* Adds a data point to the interpolator for future interpolation
* @param x The anchor point where this data is located
* @param d A vector containing multiple "y" values to be interpolated (columns)
*/
void addDataPoint(double x, std::vector<double> &d) {
// just add it to the map
data[x] = d;
}
/**
* Interpolates our data sequence at a given point, for a given column of data
* @param x The anchor point to interpolate at
* @param column The column we want to interpolate on
* @return y The interpolated value for this column
*/
double interpolate(double x, unsigned int column) {
// loop through all the keys in the map
// to find one that is greater than our intended value
std::map<double, std::vector<double> >::iterator it = data.begin();
bool found = false;
while(it != data.end() && !found) {
if(it->first >= x) {
found = true;
break;
}
// advance the iterator
it++;
}
// check to see if we're outside the data range
if(it == data.begin()) {
return data.begin()->second[column];
}
else if(it == data.end()) {
// move the point back one, as end() points past the list
it--;
return it->second[column];
}
// check to see if we landed on a given point
else if(it->first == x) {
return it->second[column];
}
// nope, we're in the range somewhere
// collect some values
double xb = it->first;
double yb = it->second[column];
it--;
double xa = it->first;
double ya = it->second[column];
// and calculate the result!
// formula from Wikipedia
return (ya + (yb - ya) * (x - xa) / (xb - xa));
}
private:
std::map<double, std::vector<double> > data;
};
@ITISAGLN
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Could you please add an example on how to use this class?

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