Revision 392ae21a013fb3f518e8f9eb8efb458a55a2eca2 authored by HwB on 09 April 2011, 00:00:00 UTC, committed by Gabor Csardi on 09 April 2011, 00:00:00 UTC
1 parent 162b332
bisect.R
##
## b i s e c t . R
##
bisect <- function(f, a, b, maxiter=100, tol=.Machine$double.eps^0.5)
# Bisection search for zero of a univariate function in a bounded interval
{
if (f(a)*f(b) > 0) stop("f(a) and f(b) must have different signs.")
x1 <- min(a, b); x2 <- max(a,b)
xm <- (x1+x2)/2.0
n <- 0
while (abs(x1-x2)/2.0 > tol) {
n <- n+1
if (abs(f(xm)) <= tol) break
if (f(x1)*f(xm) < 0) {
x2 <- xm
} else {
x1 <- xm
}
xm <- (x1+x2)/2.0 # xm <- x1 - f(x1) * (x2-x1) / (f(x2)-f(x1))
if (n >= maxiter) break
}
return(list(root=xm, f.root=f(xm), iter=n, estim.prec=abs(x1-x2)/2.0))
}
regulaFalsi <- function(f, a, b, maxiter=100, tol=.Machine$double.eps^0.5)
#Regula Falsi search for zero of a univariate function in a bounded interval
{
x1 <- a; x2 <- b
f1 <- f(x1); f2 <- f(x2)
if (f1*f2 > 0) stop("f(a) and f(b) must have different signs.")
m <- 0.5 # Illinois rule
niter <- 0
while (abs(x2-x1) >= tol && niter <= maxiter) {
niter <- niter + 1
z <- (x1*f2-x2*f1)/(f2-f1); fz <- f(z)
if(fz*f2 < 0) {
x1 <- x2; f1 <- f2
x2 <- z; f2 <- fz
} else {
# m <- f2/(f2+fz) # Pegasus rule
# m <- if (1-fz/f2 > 0) 1-fz/f2 else 0.5 # Andersen/Bjoerk
f1 <- m*f1
x2 <- z; f2 <- fz
}
}
if (niter > maxiter && abs(x2-x1) >= tol)
cat("regulaFalsi stopped without converging.\n")
return(list(zero=z, fzero=fz, niter=niter, estim.prec=x1-x2))
}
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