# expit: Expit and Logit. In rje: Miscellaneous Useful Functions for Statistics

 expit R Documentation

## Expit and Logit.

### Description

Functions to take the expit and logit of numerical vectors.

### Usage

```expit(x)

logit(x)
```

### Arguments

 `x` vector of real numbers; for `logit` to return a sensible value these should be between 0 and 1.

### Details

`logit` implements the usual logit function, which is

logit(x) = log(x/(1-x)),

and `expit` its inverse:

expit(x) = e^x/(1+e^x).

It is assumed that `logit(0) = -Inf` and `logit(1) = Inf`, and correspondingly for `expit`.

### Value

A real vector corresponding to the expits or logits of `x`

### Functions

• `logit`: logit function

### Warning

Choosing very large (positive or negative) values to apply to `expit` may result in inaccurate inversion (see example below).

Robin Evans

### Examples

```
x = c(5, -2, 0.1)
y = expit(x)
logit(y)

# Beware large values!
logit(expit(100))
```

rje documentation built on Nov. 12, 2022, 9:06 a.m.