UnirootAll {DescTools} | R Documentation |

The function `UnirootAll`

searches the interval from lower to upper
for several roots (i.e., zero's) of a function `f`

with respect to
its first argument.

```
UnirootAll(f, interval, lower = min(interval), upper = max(interval),
tol = .Machine$double.eps^0.5, maxiter = 1000, n = 100, ...)
```

`f` |
the function for which the root is sought. |

`interval` |
a vector containing the end-points of the interval to be searched for the root. |

`lower` |
the lower end point of the interval to be searched. |

`upper` |
the upper end point of the interval to be searched. |

`tol` |
the desired accuracy (convergence tolerance). |

`maxiter` |
the maximum number of iterations. |

`n` |
number of subintervals in which the root is sought. |

`...` |
additional named or unnamed arguments to be passed to |

`f`

will be called as `f(x, ...)`

for a numeric value of `x`

.

Run `demo(Jacobandroots)`

for an example of the use of `UnirootAll`

for steady-state analysis.

See also second example of `gradient`

This example is discussed in the book by Soetaert and Herman (2009).

a vector with the roots found in the interval

This is a verbatim copy from rootSolve::uniroot.all (v. 1.7).

The function calls `uniroot`

, the basic R-function.

It is not guaranteed that all roots will be recovered.

This will depend on `n`

, the number of subintervals in which the
interval is divided.

If the function "touches" the X-axis (i.e. the root is a saddle point), then this root will generally not be retrieved. (but chances of this are pretty small).

Whereas `unitroot`

passes values one at a time to the function,
`UnirootAll`

passes a vector of values to the function.
Therefore `f`

should be written such that it can handle a vector of values.
See last example.

Karline Soetaert <karline.soetaert@nioz.nl>

`uniroot`

for more information about input.

```
## =======================================================================
## Mathematical examples
## =======================================================================
# a well-behaved case...
fun <- function (x) cos(2*x)^3
curve(fun(x), 0, 10,main = "UnirootAll")
All <- UnirootAll(fun, c(0, 10))
points(All, y = rep(0, length(All)), pch = 16, cex = 2)
# a difficult case...
f <- function (x) 1/cos(1+x^2)
AA <- UnirootAll(f, c(-5, 5))
curve(f(x), -5, 5, n = 500, main = "UnirootAll")
points(AA, rep(0, length(AA)), col = "red", pch = 16)
f(AA) # !!!
## =======================================================================
## Vectorisation:
## =======================================================================
# from R-help Digest, Vol 130, Issue 27
# https://stat.ethz.ch/pipermail/r-help/2013-December/364799.html
integrand1 <- function(x) 1/x*dnorm(x)
integrand2 <- function(x) 1/(2*x-50)*dnorm(x)
integrand3 <- function(x, C) 1/(x+C)
res <- function(C) {
integrate(integrand1, lower = 1, upper = 50)$value +
integrate(integrand2, lower = 50, upper = 100)$value -
integrate(integrand3, C = C, lower = 1, upper = 100)$value
}
# uniroot passes one value at a time to the function, so res can be used as such
uniroot(res, c(1, 1000))
# Need to vectorise the function to use UnirootAll:
res <- Vectorize(res)
UnirootAll(res, c(1,1000))
```

[Package *DescTools* version 0.99.51 Index]