# R/interEllipR.R In RLeafAngle: Estimates, Plots and Evaluates Leaf Angle Distribution Functions, Calculates Extinction Coefficients

#### Documented in interEllipR

```#' Compute the fraction leaf area for rotated-ellipsoidal function given leaf angle intervals (in degree) and the parameters.
#' @description Compute the fraction leaf area given leaf angle intervals (in degree) and the parameters of rotated-ellipsoidal function.
#' @param AngleLower The lower limit of leaf angle intervals in degree.
#' @param AngleUpper The upper limit of leaf angle intervals in degree.
#' @param lambdaR The parameter of rotated-ellipsoidal function.
#' @return Compute the fraction leaf area of rotated-ellipsoidal function.
#' @author Wei-Min Wang (wmwang AT gmail.com)
#' @references  Wang, W. M., Li, Z. L., & Su, H. B. (2007).
#' Comparison of leaf angle distribution functions: effects on extinction coefficient and
#' fraction of sunlit foliage. Agricultural and Forest Meteorology, 143(1), 106-122.
#' @examples
#' interEllipR(40,50,1.1)
#' @export
#'

interEllipR<-function(AngleLower, AngleUpper, lambdaR)
{
{
if((lambdaER-1)<1*10**(-5))
{
delta<-2
}
else
{
if(lambdaER>1)
{
emiga<-(1-lambdaER**(-2))**(0.5)
delta<-lambdaER+(log((1+emiga)/(1-emiga))/(2*emiga*lambdaER))
}
else
{
emiga<-(1-lambdaER**(2))**(0.5)
delta<-lambdaER+asin(emiga)/emiga
}
}
up<-2*(lambdaER**3.0)*cos(x)
#delta<-lamdaE+1.774*(lamdaE+1.182)**(-0.733)
down<-delta*(sin(x)**2+lambdaER**2*cos(x)**2)**2
up/down
}
pi180<-pi/180.0