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\name{solve.QP}
\alias{solve.QP}
\title{Solve a Quadratic Programming Problem}
\description{
This routine implements the dual method of Goldfarb and Idnani (1982,
1983) for solving quadratic programming problems of the form
\eqn{\min(-d^T b + 1/2 b^T D b)}{min(-d^T b + 1/2 b^T D b)} with the
constraints \eqn{A^T b >= b_0}.
}
\usage{
solve.QP(Dmat, dvec, Amat, bvec, meq=0, factorized=FALSE)
}
\arguments{
\item{Dmat}{
matrix appearing in the quadratic function to be minimized.
}
\item{dvec}{
vector appearing in the quadratic function to be minimized.
}
\item{Amat}{
matrix defining the constraints under which we want to minimize the
quadratic function.
}
\item{bvec}{
vector holding the values of \eqn{b_0} (defaults to zero).
}
\item{meq}{
the first \code{meq} constraints are treated as equality
constraints, all further as inequality constraints (defaults to 0).
}
\item{factorized}{
logical flag: if \code{TRUE}, then we are passing
\eqn{R^{-1}}{R^(-1)} (where \eqn{D = R^T R}) instead of the matrix
\eqn{D} in the argument \code{Dmat}.
}
}
\value{
a list with the following components:
\item{solution}{
vector containing the solution of the quadratic programming problem.
}
\item{value}{
scalar, the value of the quadratic function at the solution
}
\item{unconstrained.solution}{
vector containing the unconstrained minimizer of the quadratic
function.
}
\item{iterations}{
vector of length 2, the first component contains the number of
iterations the algorithm needed, the second indicates how often
constraints became inactive after becoming active first.
}
\item{Lagrangian}{
vector with the Lagragian at the solution.
}
\item{iact}{
vector with the indices of the active constraints at the solution.
}
}
\references{
D. Goldfarb and A. Idnani (1982).
Dual and Primal-Dual Methods for Solving Strictly Convex
Quadratic Programs.
In J. P. Hennart (ed.), Numerical Analysis, Springer-Verlag,
Berlin, pages 226--239.
D. Goldfarb and A. Idnani (1983).
A numerically stable dual method for solving strictly convex quadratic
programs.
\emph{Mathematical Programming}, \bold{27}, 1--33.
}
\seealso{
\code{\link{solve.QP.compact}}
}
\examples{
##
## Assume we want to minimize: -(0 5 0) \%*\% b + 1/2 b^T b
## under the constraints: A^T b >= b0
## with b0 = (-8,2,0)^T
## and (-4 2 0)
## A = (-3 1 -2)
## ( 0 0 1)
## we can use solve.QP as follows:
##
Dmat <- matrix(0,3,3)
diag(Dmat) <- 1
dvec <- c(0,5,0)
Amat <- matrix(c(-4,-3,0,2,1,0,0,-2,1),3,3)
bvec <- c(-8,2,0)
solve.QP(Dmat,dvec,Amat,bvec=bvec)
}
\keyword{optimize}
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