The function is f(s,t) = ( a1*t + a2*t^2 + ( a3*t + a4*t^2 )*d1*s^2*t^2 + (a5*t + a6*t^2)*d1^2*b^4*t^4 )*exp(-0.5*d1*s^2*t^2) + a8
where a1,a2,...,a8,d1 are some constants (can be positive or negative), which are computed from a given set of data. The objective is to find the minimum value of s >0.5, which satisfies f(s,t) >0 where t can be any value on the real line. It may be that such s does not exist for the given dataset If the conditions f(s,t)>0 and s>0.5 were not needed, then optim could be used to find the minimum values for both (s,t) with the range setting at -Inf and Inf. I suppose one way to do it (I haven't tried out) is to substitute the values of (s,t) found and see if they satisfy f(s,t)>0, but it may be that s found is < 0.5, and there is another one just >0.5 There are also other potential problems and computational disadvantages. 2008/4/24 Paul Smith <[EMAIL PROTECTED]>: > On Wed, Apr 23, 2008 at 8:51 PM, Kevin Lu <[EMAIL PROTECTED]> wrote: > > I need to find the minimum value of the parameter, s, such that the > function > > f(s,t) > 0 (where -Inf < t < Inf) > > > > I've looked into optim, constrOptim and others but they don't seem to do > > this. Des anyone have some suggestions? > > In order to allow us to help you, please send us a minimal example. > > Paul > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
