# weight.funs: Weight Functions Psi, Rho, Chi In robust: Port of the S+ "Robust Library"

## Description

These functions compute the weights used by lmRob and its associated methods.

## Usage

 ```1 2 3 4``` ```psi.weight(x, ips = 1, xk = 1.06) rho.weight(x, ips = 1, xk = 1.06) psp.weight(x, ips = 1, xk = 1.06) chi.weight(x, ips = 1, xk = 1.06) ```

## Arguments

 `x` a numeric vector. `ips` integer determining the weight function: `ips = 1`"optimal" , `ips = 2`rescaled bisquare , `ips = 3`Huber , `ips = 4`smoothed Huber , which is currently only available for `psi.*()` and its derivative `psp.*()`. `xk` a numeric value specifying the tuning constant.

## Details

See the section “Theoretical Details”, p. 58-59, in chapter 2 of ‘Robust.pdf’.

## Value

a numeric vector, say `r` of the same length as `x`, containing the function values r[i] = f(x[i]).

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11``` ```x <- seq(-4,4, length=401) f.x <- cbind(psi = psi.weight(x), psp = psp.weight(x), chi = chi.weight(x), rho = rho.weight(x)) es <- expression(psi(x), {psi*minute}(x), chi(x), rho(x)) leg <- as.expression(lapply(seq_along(es), function(i) substitute(C == E, list(C=colnames(f.x)[i], E=es[[i]])))) matplot(x, f.x, type = "l", lwd = 1.5, main = "psi.weight(.) etc -- 'optimal'") abline(h = 0, v = 0, lwd = 2, col = "#D3D3D380") # opaque gray legend("bottom", leg, inset = .01, lty = 1:4, col = 1:4, lwd = 1.5, bg = "#FFFFFFC0") ```

### Example output

```Loading required package: fit.models
Registered S3 methods overwritten by 'robust':
method              from
plot.covfm          fit.models
print.covfm         fit.models
summary.covfm       fit.models
print.summary.covfm fit.models
rlm is already registered in the fit.models registry
covfm is already registered in the fit.models registry

Attaching package: ‘robust’

The following objects are masked from ‘package:fit.models’:

ddPlot.covfm, distancePlot.covfm, ellipsesPlot.covfm,
screePlot.covfm
```

robust documentation built on May 2, 2019, 5:20 p.m.