#===> extract a p-value from coxph <===#
local.coxph.test <- function(coxph.fit, pos, C=NA, d=NA, sign.digits=3){
  # checking H_0: C*beta.hat = c
  # coxph.fit is a coxph model
  # pos is the position numbers of the parameters of interest
  # C is a q-by-p matrix
  # d is a q-by-1 matrix
	n <- length(pos)
	if(is.na(C)){
		C <- matrix(0, n, n)
		for(i in 1:n)
			C[i,i] <- 1
	} else {
		if(dim(C)[1] != n)
			stop("C has improper dimensions\n")
	}
	if(is.na(d))
		d <- matrix(0, n, 1)
	if(dim(d)[1] != dim(C)[1])
		stop("C and d do not have appropriate dimensions\n")
	I. <- coxph.fit$var[pos,pos]
	est <- matrix(as.vector(coxph.fit$coeff[pos]), dim(C)[2])
	X <- as.numeric( t(C%*%est - d) %*%
		solve( t(C) %*% I. %*% C )  %*%
		(C%*%est - d) )
	signif(1-pchisq(X, dim(C)[1]), sign.digits)
}
local.p.test <- local.coxph.test