mono.con {mgcv} R Documentation

Monotonicity constraints for a cubic regression spline

Description

Finds linear constraints sufficient for monotonicity (and optionally upper and/or lower boundedness) of a cubic regression spline. The basis representation assumed is that given by the `gam`, `"cr"` basis: that is the spline has a set of knots, which have fixed x values, but the y values of which constitute the parameters of the spline.

Usage

```mono.con(x,up=TRUE,lower=NA,upper=NA)
```

Arguments

 `x` The array of knot locations. `up` If `TRUE` then the constraints imply increase, if `FALSE` then decrease. `lower` This specifies the lower bound on the spline unless it is `NA` in which case no lower bound is imposed. `upper` This specifies the upper bound on the spline unless it is `NA` in which case no upper bound is imposed.

Details

Consider the natural cubic spline passing through the points: (x_i,p_i), i=1..n. Then it is possible to find a relatively small set of linear constraints on p sufficient to ensure monotonicity (and bounds if required): Ap>=b. Details are given in Wood (1994). This function returns a list containing `A` and `b`.

Value

The function returns a list containing constraint matrix `A` and constraint vector `b`.

Author(s)

Simon N. Wood simon.wood@r-project.org

References

Gill, P.E., Murray, W. and Wright, M.H. (1981) Practical Optimization. Academic Press, London.

Wood, S.N. (1994) Monotonic smoothing splines fitted by cross validation SIAM Journal on Scientific Computing 15(5):1126-1133

`mgcv ` `pcls`

Examples

```## see ?pcls
```

[Package mgcv version 1.3-12 Index]