[R-sig-dyn-mod] Different solutions using deSolve::ode() with 32 and 64 Bit systems: Problem for sensitivity analysis

[Johannes Friedrich]

Dear Ladies and Gentlemen,

during the last days I made a strange observation concerning the package 
"FME" and "deSolve".
I used a local sensitivity analysis in my R-package and also made a 
little example in the manual of the package. To check the performance, I 
sent my package to the win-builder and I compared the results between 
examples_i386 and examples_x64. And the result was, that the sensitivity 
analysis using the function /FME::sensFun() /produces NOT the same using 
R 32 Bit or R 64 Bit.

I then made a little comparison and a reproducible example (from the FME 
vignette):
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
/library("deSolve")//
//library("FME")//
//pars <- list(gmax = 0.5, eff = 0.5, ks = 0.5, rB = 0.01, dB = 0.01)//
//
//solveBact <- function(pars, times=seq(0, 50, by=0.5)) {//
//    derivs <- function(t, state, pars) {//
//        with(as.list(c(state, pars)), {//
//            dBact <- gmax*eff*Sub/(Sub+ks)*Bact - dB*Bact - rB*Bact//
//              dSub <- -gmax*Sub/(Sub+ks)*Bact + dB*Bact//
////
//                return(list(c(dBact, dSub), TOC = Bact + Sub))//
//
//        })//
//      }//
//    state <- c(Bact = 0.1, Sub = 100)//
//      return(ode(y = state, times = times, func = derivs, parms = pars))//
//}//
//
//out <- solveBact(pars)//
//
//SnsBact <- sensFun(func = solveBact, //
//                  parms = pars, //
//                  sensvar = "Bact", //
//                  varscale = 1)/
- - - - - - - - - - - - - - - - - - - - - - - - - - - -
Running  this little example with R (3.3.0) 32 Bit and 64 Bit gives not 
the same results. You can check this, e.g.
/identical(SnSBact$gmax_x64, SnSBact$gmax_x32)/.
Also the solution of the differential equations using /deSolve::ode()/ 
are not the same (/identical(out[,"TOC"], out_x64[,"TOC"])/)
In this example this has only little effects, but with bigger models 
(like my package) the differences are enormous.

  * Has someone ever detected the same problems?

  * Comes the problem for the sensitivity analysis from the different
    ODE solutions, or is the problem also part of the /FME::sensFun()/
    function?

Thanks for any pointers,
Johannes

-- 
Johannes Friedrich
University of Bayreuth
Chair of Geomorphology
95440 Bayreuth, Germany
Tel. +49-921-55-2054
Fax +49-921-55-2314

http://www.geomorph.uni-bayreuth.de/


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