public void Test_VandermondeMatrix_4_Inverse()
{
// (-2, -39), (0, 3), (1, 6), (3, 36)
VandermondeMatrix vm = new VandermondeMatrix(-2, 0, 1, 3);
Vector y = new Vector(new double[] { -39, 3, 6, 36 });
double determinant = vm.GetDeterminant();
Assert.NotEqual(0, determinant);
Matrix m = vm.GetInverse();
Vector actual = m * y;
// p(x) = 2x^3-4x^2+5x+3
Assert.Equal(3, actual[0]);
Assert.Equal(5, actual[1]);
Assert.Equal(-4, actual[2]);
Assert.Equal(2, actual[3]);
}
private Vector GetCoeffs(double[] data)
{
Polynomial polynomial = new Polynomial();
int length = data.Length / 2;
double[] x = new double[length];
double[] y = new double[length];
for (int i = 0; i < length; i++)
{
x[i] = data[i * 2];
y[i] = data[i * 2 + 1];
}
VandermondeMatrix vm = new VandermondeMatrix(x);
Vector v = new Vector(y);
return(vm.GetInverse() * v);
}
public void Test_VandermondeMatrix_4_Inverse2()
{
// (0, 3), (1, 6), (3, 36), (4, 9)
VandermondeMatrix vm = new VandermondeMatrix(0, 1, 3, 4);
Vector y = new Vector(new double[] { 3, 6, 36, 9 });
double determinant = vm.GetDeterminant();
Assert.NotEqual(0, determinant);
Matrix m = vm.GetInverse();
Vector actual = m * y;
// p(x) = -4.5x^3 + 22x^2 -14.5x + 3
Assert.Equal(3, actual[0]);
Assert.Equal(-14.5, actual[1]);
Assert.Equal(0, 22 - actual[2], 14);
Assert.Equal(-4.5, actual[3]);
}