This function creates the basis function of a second-order (linear) splines at a user-specific set of break points.

## Usage

```
make_basis(
x,
xname = "x",
internal = NULL,
boundary = range(x),
degree = 1L,
warn = TRUE
)
```

## Arguments

- x
numeric vector

- xname
predictor name. Default is

`"x"`

- internal
a vector of internal knots, excluding boundary knots

- boundary
vector of external knots

- degree
the degree of the spline. The broken stick model requires linear splines, so the default is

`degree = 1`

. Setting`degree = 0`

yields (crisp) dummy coding, and one column less than for`degree = 1`

.- warn
a logical indicating whether warnings from

`splines::bs()`

should be given.

## Value

A matrix with `length(x)`

rows and `length(breaks)`

columns, with some extra attributes described by `bs()`

.