[R] Issue with asin()

[Berend Hasselman]

On 19-03-2012, at 12:42, Letnichev wrote:

> Hello everyone,
> 
> I am working for a few days already on a basic algorithm, very common in
> applied agronomy, that aims to determine the degree-days necessary for a
> given individual to reach a given growth stade. The algorithm (and context)
> is explained here:  http://www.oardc.ohio-state.edu/gdd/glossary.htm , and
> so I implemented my function in R as follows:
> 
> DD <- function(Tmin, Tmax, Tseuil, meanT, method = "DDsin")
> ### function that calculates the degree-days based on
> ### minimum and maximum recorded temperatures and the
> ### minimal threshold temperature (lower growth temperature)
> 	{
> 	### method arcsin
> 	if(method == "DDsin"){
> 		cond1 <- (Tmax <= Tseuil)
> 		cond2 <- (Tmin >= Tseuil)
> 		amp <- ((Tmax - Tmin) / 2)
> 		print((Tseuil-meanT)/amp)
> 		alpha <- asin((Tseuil - meanT) / amp)
> 		DD_ifelse3 <- ((1 / pi) * ((meanT - Tseuil) * ((pi/2) - alpha)) +
> amp*cos(alpha))
> 		
> 		DD <- ifelse(cond1, 0, ifelse(cond2, (meanT - Tseuil), DD_ifelse3))
> 	}
> 
> 	### method (Tmin + Tmax) / 2
> 	else if(method == "DDt2"){
> 		cond1 <- (meanT > Tseuil)
> 		DD <- ifelse(cond1,(meanT - Tseuil),0)
> 		}
> 
> 	else{
> 		stop("\nMethod name is invalid.\nMethods available = DDsin (sinus) or DDt2
> (mean)\n")
> 		}
> 	return(DD)
> }
> 
> BUT! When I try to process random data:
> 
> library(reshape2)
> library(plyr)
> 
> station <- rep(c("station1","station2","station3"), 20)
> values_min <- sample(-5:20, size = 60, replace = T)
> values_max <- sample(20:40, size = 60, replace = T)
> meanT <- ((values_min+values_max)/2)
> d <- data.frame(station,values_min,values_max,meanT)
> names(d) <- c("station", "values_min","values_max","meanT")
> 
> x<-ddply(d, .(station), transform, t1 =
> cumsum(DD(values_min,values_max,0,meanT)))
> 
> I get a warning on my alpha calculation (NaN produced); indeed, the values I
> give as argument to asin() are out of the range [-1:1], as the print()
> reveals. I can't figure out how to solve this issue, because the same
> algorithm works in Excel (visual basic).

That doesn't mean that Excel and/or Visual Basic gives correct answers.

With the same input?
Then what does Excel say that asin(-7.4) evaluates to?
I tried asin(-1.2) and asin(-7.4)  in LibreOffice Calc (3.5.0) and got #VALUE! (Error: wrong data type) twice.

You'll have to present correct input to asin()  if you want to avoid the NaN's.

Berend

> It is very annoying, especially because it seems that no occurence of such
> error using that algorithm can be found on Internet.
> Any help is welcome :) Thanks for your time
> 
> P.
> 
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