pmlpp/mlpp/pca/pca.cpp
2023-01-24 18:12:23 +01:00

57 lines
1.5 KiB
C++

//
// PCA.cpp
//
// Created by Marc Melikyan on 10/2/20.
//
#include "pca.h"
#include "../lin_alg/lin_alg.h"
#include "../data/data.h"
#include <iostream>
#include <random>
namespace MLPP{
PCA::PCA(std::vector<std::vector<double>> inputSet, int k)
: inputSet(inputSet), k(k)
{
}
std::vector<std::vector<double>> PCA::principalComponents(){
LinAlg alg;
Data data;
auto [U, S, Vt] = alg.SVD(alg.cov(inputSet));
X_normalized = data.meanCentering(inputSet);
U_reduce.resize(U.size());
for(int i = 0; i < k; i++){
for(int j = 0; j < U.size(); j++){
U_reduce[j].push_back(U[j][i]);
}
}
Z = alg.matmult(alg.transpose(U_reduce), X_normalized);
return Z;
}
// Simply tells us the percentage of variance maintained.
double PCA::score(){
LinAlg alg;
std::vector<std::vector<double>> X_approx = alg.matmult(U_reduce, Z);
double num, den = 0;
for(int i = 0; i < X_normalized.size(); i++){
num += alg.norm_sq(alg.subtraction(X_normalized[i], X_approx[i]));
}
num /= X_normalized.size();
for(int i = 0; i < X_normalized.size(); i++){
den += alg.norm_sq(X_normalized[i]);
}
den /= X_normalized.size();
if(den == 0){
den+=1e-10; // For numerical sanity as to not recieve a domain error
}
return 1 - num/den;
}
}