uobyqa {minqa} | R Documentation |
An R interface to the uobyqa implementation of Powell
Description
The purpose of uobyqa
is to minimize a function of many variables
by a trust region method that forms quadratic models by interpolation.
Usage
uobyqa(par, fn, control = list(), ...)
Arguments
par |
A numeric vector of starting estimates. |
fn |
A function that returns the value of the objective at the
supplied set of parameters |
control |
An optional list of control settings. See the details section for the names of the settable control values and their effect. |
... |
Further arguments to be passed to |
Details
Functions fn
must return a numeric value.
The control
argument is a list. Possible named values in the
list and their defaults are:
- rhobeg
-
rhobeg
andrhoend
must be set to the initial and final values of a trust region radius, so both must be positive with0 < rhoend < rhobeg
. Typicallyrhobeg
should be about one tenth of the greatest expected change to a variable. - rhoend
-
The smallest value of the trust region radius that is allowed. If not defined, then 1e-6 times the value set for
rhobeg
will be used. - iprint
-
The value of
iprint
should be set to an integer value in0, 1, 2, 3, ...
, which controls the amount of printing. Specifically, there is no output ifiprint=0
and there is output only at the start and the return ifiprint=1
. Otherwise, each new value ofrho
is printed, with the best vector of variables so far and the corresponding value of the objective function. Further, each new value of the objective function with its variables are output ifiprint=3
. Ifiprint > 3
, the objective function value and corresponding variables are output everyiprint
evaluations. Default value is0
. - maxfun
-
The maximum allowed number of function evaluations. If this is exceeded, the method will terminate.
Powell's Fortran code has been slightly modified (thanks to Doug Bates for help on this) to avoid use of PRINT statements. Output is now via calls to C routines set up to work with the routines BOBYQA, NEWUOA and UOBYQA.
Value
A list with components:
par |
The best set of parameters found. |
fval |
The value of the objective at the best set of parameters found. |
feval |
The number of function evaluations used. |
ierr |
An integer error code. A value of zero indicates success. Other values (consistent with BOBYQA values) are
|
msg |
A message describing the outcome of UOBYQA |
References
M. J. D. Powell, "The uobyqa software for unconstrained optimization without derivatives", in Large-Scale Nonlinear Optimization, Series: Nonconvex Optimization and Its Applications , Vol. 83, Di Pillo, Gianni; Roma, Massimo (Eds.) 2006, New York: Springer US.
M. J. D. Powell, "Developments of uobyqa for minimization without derivatives", IMA Journal of Numerical Analysis, 2008; 28: 649-664.
Description was taken from comments in the Fortran code of M. J. D. Powell on which minqa is based.
See Also
Examples
fr <- function(x) { ## Rosenbrock Banana function
100 * (x[2] - x[1]^2)^2 + (1 - x[1])^2
}
(x3 <- uobyqa(c(1, 2), fr))
## => optimum at c(1, 1) with fval = 0
# check the error exits
# too many iterations
x3e<-uobyqa(c(1, 2), fr, control = list(maxfun=50))
str(x3e)
# To add if we can find them -- examples of ierr = 3.