## Given time points covariate and order of fit for Legendre polynomials, return matrix 'M' containing the polynomials of standardized time. 'M' is order t (number of time points) by k (order of Legendre polynomials).

## Arguments 
##	t: a vector of time, age or days
## 	n: order of polynomials
##      tmax: max time (optional)
##      tmin: min time (optional)

## Literature: Mrode, R.A. 2005. Linear Models for the Prediction of Animal Breeding Values. CAB International, Oxon, UK.

## Author: Gota Morota <morota at wisc dot edu>
## Created: 31-Mar-2010
## Last-Modified: 2-Apr-2010
## License: GPLv3 or later

`stdtime` <-
function(t, n, tmax, tmin){
	if(missing(tmax)) {
   	  tmax <- t[which.max(t)]
	}
        if(missing(tmin)) {
            tmin <- t[which.min(t)]
        }
	
	N <- n+1
	M <- matrix(0, nrow=length(t), ncol=N)
        a <- -1 + 2*(t-tmin)/(tmax - tmin)
        M[,1] <- 1
	
	for (i in 2:N){
		M[,i] <- a^(i-1)
	}
	
	return(M)
}