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Copy pathGaussian.java
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78 lines (67 loc) · 2.16 KB
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package com.thealgorithms.maths;
import java.util.ArrayList;
public class Gaussian {
public static ArrayList<Double> gaussian(
int mat_size,
ArrayList<Double> matrix
) {
ArrayList<Double> answerArray = new ArrayList<Double>();
int i, j = 0;
double[][] mat = new double[mat_size + 1][mat_size + 1];
double[][] x = new double[mat_size][mat_size + 1];
// Values from arraylist to matrix
for (i = 0; i < mat_size; i++) {
for (j = 0; j <= mat_size; j++) {
mat[i][j] = matrix.get(i);
}
}
mat = gaussianElimination(mat_size, i, mat);
answerArray = valueOfGaussian(mat_size, x, mat);
return answerArray;
}
// Perform Gaussian elimination
public static double[][] gaussianElimination(
int mat_size,
int i,
double[][] mat
) {
int step = 0;
for (step = 0; step < mat_size - 1; step++) {
for (i = step; i < mat_size - 1; i++) {
double a = (mat[i + 1][step] / mat[step][step]);
for (int j = step; j <= mat_size; j++) {
mat[i + 1][j] = mat[i + 1][j] - (a * mat[step][j]);
}
}
}
return mat;
}
// calculate the x_1, x_2,... values of the gaussian and save it in an arraylist.
public static ArrayList<Double> valueOfGaussian(
int mat_size,
double[][] x,
double[][] mat
) {
ArrayList<Double> answerArray = new ArrayList<Double>();
int i, j;
for (i = 0; i < mat_size; i++) {
for (j = 0; j <= mat_size; j++) {
x[i][j] = mat[i][j];
}
}
for (i = mat_size - 1; i >= 0; i--) {
double sum = 0;
for (j = mat_size - 1; j > i; j--) {
x[i][j] = x[j][j] * x[i][j];
sum = x[i][j] + sum;
}
if (x[i][i] == 0) {
x[i][i] = 0;
} else {
x[i][i] = (x[i][mat_size] - sum) / (x[i][i]);
}
answerArray.add(x[i][j]);
}
return answerArray;
}
}