Revision d5bfb0e3b7a3211ff2bbe2926e5ba31aa24e4df6 authored by HwB on 09 March 2012, 00:00:00 UTC, committed by Gabor Csardi on 09 March 2012, 00:00:00 UTC
1 parent 63e8a52
laguerre.R
##
## l a g u e r r e . R Laguerre Method
##
laguerre <- function(p, x0, nmax = 25, tol = .Machine$double.eps^(1/2)) {
if (!is.numeric(p) && !is.complex(p))
stop("Argument 'p' must be a numeric or complex vector.")
if ( (!is.numeric(x0) && !is.complex(x0)) || length(x0) != 1)
stop("Argument 'x0' must be a real or complex number.")
n <- length(p) - 1
p1 <- polyder(p)
p2 <- polyder(p1)
y0 <- polyval(p, x0)
if (abs(y0) < tol) return(x0)
for (m in 1:nmax) {
a <- polyval(p1, x0) / y0
a2 <- a^2
b <- a2 - polyval(p2, x0) / y0
x <- x0 - n/(a + a/abs(a) * sqrt((n-1)*(n*b - a2)))
y <- polyval(p, x)
if (abs(y) < tol) break
x0 <- x
y0 <- y
}
if (m > nmax)
warning("Root finding process might not have converged.")
return(x)
}
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