/// <summary>
/// Compute spline coefficients for the specified x,y points.
/// This does the "natural spline" style for ends.
/// This can extrapolate off the ends of the splines.
/// You must provide points in X sort order.
/// </summary>
/// <param name="x">Input. X coordinates to fit.</param>
/// <param name="y">Input. Y coordinates to fit.</param>
/// <param name="debug">Turn on console output. Default is false.</param>
public void Fit(double[] x, double[] y)
{
// Save x and y for eval
this.xOrig = x;
this.yOrig = y;
int n = x.Length;
double[] r = new double[n]; // the right hand side numbers: wikipedia page overloads b
TriDiagonalMatrixF m = new TriDiagonalMatrixF(n);
double dx1, dx2, dy1, dy2;
// First row is different (equation 16 from the article)
dx1 = x[1] - x[0];
m.C[0] = 1.0f / dx1;
m.B[0] = 2.0f * m.C[0];
r[0] = 3 * (y[1] - y[0]) / (dx1 * dx1);
// Body rows (equation 15 from the article)
for (int i = 1; i < n - 1; i++)
{
dx1 = x[i] - x[i - 1];
dx2 = x[i + 1] - x[i];
m.A[i] = 1.0f / dx1;
m.C[i] = 1.0f / dx2;
m.B[i] = 2.0f * (m.A[i] + m.C[i]);
dy1 = y[i] - y[i - 1];
dy2 = y[i + 1] - y[i];
r[i] = 3 * (dy1 / (dx1 * dx1) + dy2 / (dx2 * dx2));
}
// Last row also different (equation 17 from the article)
dx1 = x[n - 1] - x[n - 2];
dy1 = y[n - 1] - y[n - 2];
m.A[n - 1] = 1.0f / dx1;
m.B[n - 1] = 2.0f * m.A[n - 1];
r[n - 1] = 3 * (dy1 / (dx1 * dx1));
// k is the solution to the matrix
double[] k = m.Solve(r);
// a and b are each spline's coefficients
this.a = new double[n - 1];
this.b = new double[n - 1];
for (int i = 1; i < n; i++)
{
dx1 = x[i] - x[i - 1];
dy1 = y[i] - y[i - 1];
a[i - 1] = k[i - 1] * dx1 - dy1; // equation 10 from the article
b[i - 1] = -k[i] * dx1 + dy1; // equation 11 from the article
}
}
/// <summary>
/// Compute spline coefficients for the specified x,y points.
/// This does the "natural spline" style for ends.
/// This can extrapolate off the ends of the splines.
/// You must provide points in X sort order.
/// </summary>
/// <param name="x">Input. X coordinates to fit.</param>
/// <param name="y">Input. Y coordinates to fit.</param>
/// <param name="debug">Turn on console output. Default is false.</param>
public void Fit(double[] x, double[] y)
{
// Save x and y for eval
this.xOrig = x;
this.yOrig = y;
int n = x.Length;
double[] r = new double[n]; // the right hand side numbers: wikipedia page overloads b
TriDiagonalMatrixF m = new TriDiagonalMatrixF(n);
double dx1, dx2, dy1, dy2;
// First row is different (equation 16 from the article)
dx1 = x[1] - x[0];
m.C[0] = 1.0f / dx1;
m.B[0] = 2.0f * m.C[0];
r[0] = 3 * (y[1] - y[0]) / (dx1 * dx1);
// Body rows (equation 15 from the article)
for (int i = 1; i < n - 1; i++)
{
dx1 = x[i] - x[i - 1];
dx2 = x[i + 1] - x[i];
m.A[i] = 1.0f / dx1;
m.C[i] = 1.0f / dx2;
m.B[i] = 2.0f * (m.A[i] + m.C[i]);
dy1 = y[i] - y[i - 1];
dy2 = y[i + 1] - y[i];
r[i] = 3 * (dy1 / (dx1 * dx1) + dy2 / (dx2 * dx2));
}
// Last row also different (equation 17 from the article)
dx1 = x[n - 1] - x[n - 2];
dy1 = y[n - 1] - y[n - 2];
m.A[n - 1] = 1.0f / dx1;
m.B[n - 1] = 2.0f * m.A[n - 1];
r[n - 1] = 3 * (dy1 / (dx1 * dx1));
// k is the solution to the matrix
double[] k = m.Solve(r);
// a and b are each spline's coefficients
this.a = new double[n - 1];
this.b = new double[n - 1];
for (int i = 1; i < n; i++)
{
dx1 = x[i] - x[i - 1];
dy1 = y[i] - y[i - 1];
a[i - 1] = k[i - 1] * dx1 - dy1; // equation 10 from the article
b[i - 1] = -k[i] * dx1 + dy1; // equation 11 from the article
}
}