# [R] Issue with asin()

Duncan Murdoch murdoch.duncan at gmail.com
Mon Mar 19 15:16:52 CET 2012

```On 12-03-19 7:42 AM, 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)

These look like useful diagnostics of out-of-range values, but you don't
use them before the arcsin transformation.

> 		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:

It's a good idea to use set.seed when trying to debug problems like
this.  Then you can construct a reproducible example.  I'd also suggest
getting rid of ddply at least for debugging; it makes it harder to see
what's going on.

Duncan Murdoch

>
> 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).
> 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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>
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