R/my_reg_fit.R

In erikerhardt/isogasex: Isotopic gas exchange using TDL and Licor input. Updated version of package tdllicor

#' basic SLR beta fit
#'
#' Calculate intercept and slope of a simple linear regression fit.
#'
#' @param y xxxPARAMxxx
#' @param x xxxPARAMxxx
#'
#' @return beta_hat xxxRETURNxxx
#'
my_reg_fit <-
function# basic SLR beta fit
###
(y
###
, x
###
)
{
  ##details<<
  ## Calculate intercept and slope of a simple linear regression fit.

  n <- length(x);
  y1 <- matrix(y,ncol=1);
  x1 <- cbind(matrix(rep(1,n),ncol=1), matrix(x-mean(x),ncol=1)); # centered x
  #x1 <- cbind(matrix(rep(1,n),ncol=1), matrix(x,ncol=1));
  if (qr(x1)$rank == 2) { # calculate regression line if the matrix is full rank  "0.1-16" "2012-07-10"
    beta_hat <- solve( t(x1) %*% x1 ) %*% t(x1) %*% y1; # slope correct, intercept from centered x
  } else { # is only not full rank if a single observation
    beta_hat <- c(y1,0)
  }
  y2 <- beta_hat[1] + beta_hat[2]*mean(x);
  beta_hat[1] <- beta_hat[1] - (y2-beta_hat[1]); # intercept corrected

  return( beta_hat );
  ### beta_hat
}