Three rational functions are provided in Genstat, each of which is a ratio of polynomials.

## Linear-by-linear

Y = a + b / (1 + d*X)

This produces a rectangular hyperbola.

## Quadratic-by-linear

Y = a + b/(1 + d*X) + c*X

This produces a hyperbola with non-horizontal asymptote.

## Quadratic-by-quadratic

Y = a + (b + c*X)/(1 + d*X + e*X*X)

This is a cubic curve with asymmetric maximum, falling to an asymptote.

## See also

- Standard Curves for information on general options and other curves
- Options for choosing which results to display
- Further Output for additional output subsequent to analysis
- Standard Curves with Correlated Errors for fitting curves with correlated errors
- Saving Results for further analysis
- Fitted Model for graphical display of the model
- Model Checking for diagnostic plots for model checking
- Examples of Standard Nonlinear Curves
- Exponential Curves
- Fourier Curves
- Gaussian Curves
- Growth Curves
- Nonlinear Models menu
- Nonlinear Quantile Regression menu
- FITCURVE directive
- FITNONLINEAR directive
- FIT directive
- RQNONLINEAR procedure