uniroot {stats} | R Documentation |

## One Dimensional Root (Zero) Finding

### Description

The function `uniroot`

searches the interval from `lower`

to `upper`

for a root (i.e., zero) of the function `f`

with
respect to its first argument.

### Usage

uniroot(f, interval, lower = min(interval), upper = max(interval),
tol = .Machine$double.eps^0.25, maxiter = 1000, ...)

### Arguments

`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. |

`...` |
additional arguments to `f` . |

### Details

Either `interval`

or both `lower`

and `upper`

must be
specified. The function uses Fortran subroutine ‘`"zeroin"`’ (from
Netlib) based on algorithms given in the reference below.

If the algorithm does not converge in `maxiter`

steps, a warning
is printed and the current approximation is returned.

### Value

A list with four components: `root`

and `f.root`

give the
location of the root and the value of the function evaluated at that
point. `iter`

and `estim.prec`

give the number of iterations
used and an approximate estimated precision for `root`

.

### References

Brent, R. (1973)
*Algorithms for Minimization without Derivatives.*
Englewood Cliffs, NJ: Prentice-Hall.

### See Also

`polyroot`

for all complex roots of a polynomial;
`optimize`

, `nlm`

.

### Examples

f <- function (x,a) x - a
str(xmin <- uniroot(f, c(0, 1), tol = 0.0001, a = 1/3))
str(uniroot(function(x) x*(x^2-1) + .5, low = -2, up = 2, tol = 0.0001),
dig = 10)
str(uniroot(function(x) x*(x^2-1) + .5, low = -2, up =2 , tol = 1e-10 ),
dig = 10)
## Find the smallest value x for which exp(x) > 0 (numerically):
r <- uniroot(function(x) 1e80*exp(x) -1e-300,,-1000,0, tol=1e-20)
str(r, digits= 15)##> around -745.1332191
exp(r$r) # = 0, but not for r$r * 0.999...
minexp <- r$r * (1 - .Machine$double.eps)
exp(minexp) # typically denormalized

[Package

*stats* version 2.1.0

Index]