R help - Nov 2004 - optimize in very small values

I hope you will forgive me this simple question on titration.
I'm trying to find very small values from the algorithm below, which I 
believe is
correctly formatted, and the constants are also correct. When SID goes over 
ATOT, fitted vales are
much too low compared to the literature. I guess I must be using optimize 
in a wrong way but cannot find out how to improve it. I'm on windows, R 
2.0. Best wishes
Troels Ring, Aalborg

ATOT <- 0.019
KA <- 3e-7
KW <- 4.4e-14
SID <- 0.01

ff <- function(H,KA,SID,ATOT)
{H^3 + (KA+SID)*H^2+(KA*(SID-ATOT)-KW)*H- KA*KW}
-log10(optimize(ff,c(0,.1),tol=.Machine$double.eps,KA=KA,SID=SID,ATOT=ATOT)$minimum)

Troels Ring wrote:
> I hope you will forgive me this simple question on titration.
> I'm trying to find very small values from the algorithm below, which I 
> believe is
> correctly formatted, and the constants are also correct. When SID goes 
> over ATOT, fitted vales are
> much too low compared to the literature. I guess I must be using 
> optimize in a wrong way but cannot find out how to improve it. I'm on 
> windows, R 2.0. Best wishes
> Troels Ring, Aalborg
> 
> ATOT <- 0.019
> KA <- 3e-7
> KW <- 4.4e-14
> SID <- 0.01
> 
> ff <- function(H,KA,SID,ATOT)
> {H^3 + (KA+SID)*H^2+(KA*(SID-ATOT)-KW)*H- KA*KW}
>
-log10(optimize(ff,c(0,.1),tol=.Machine$double.eps,KA=KA,SID=SID,ATOT=ATOT)$minimum)
Well, whether the usage is appropriate depends on the problem. At least 
I have not understood what you are going to minimize...

Uwe Ligges


> 
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Dear friends - just to prevent further loss of time on the problem below - 
I realized that it was really a root finding exercise and not a 
minimization - uniroot solved the problem.
Sorry for the confusion.
Best wishes
Troels

At 00:06 11/23/04, you wrote:
>I hope you will forgive me this simple question on titration.
>I'm trying to find very small values from the algorithm below, which I 
>believe is
>correctly formatted, and the constants are also correct. When SID goes 
>over ATOT, fitted vales are
>much too low compared to the literature. I guess I must be using optimize 
>in a wrong way but cannot find out how to improve it. I'm on windows, R 
>2.0. Best wishes
>Troels Ring, Aalborg
>
>ATOT <- 0.019
>KA <- 3e-7
>KW <- 4.4e-14
>SID <- 0.01
>
>ff <- function(H,KA,SID,ATOT)
>{H^3 + (KA+SID)*H^2+(KA*(SID-ATOT)-KW)*H- KA*KW}
>-log10(optimize(ff,c(0,.1),tol=.Machine$double.eps,KA=KA,SID=SID,ATOT=ATOT)$minimum)
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html