Quartic
A fourth-degree polynomial. Use it as an empirical curve when lower-degree polynomials leave a pattern in the residuals.
Parameters
- Coefficient of x⁴.
- Coefficient of x³.
- Coefficient of x².
- Coefficient of x.
- Value of y at x = 0.
Tips
- A quartic has five parameters, so it needs at least five points, and more to estimate the uncertainty scale from the residuals.
- Polynomial coefficients are usually strongly correlated; the model uncertainty band shows how well the curve itself is determined.
- Avoid extrapolating: a high-degree polynomial can turn sharply just outside the fitted range.