Re: FindRoot with Logarithmic terms

*To*: mathgroup at smc.vnet.net*Subject*: [mg116025] Re: FindRoot with Logarithmic terms*From*: psycho_dad <s.nesseris at gmail.com>*Date*: Sat, 29 Jan 2011 05:28:45 -0500 (EST)*References*: <ihu8is$1pj$1@smc.vnet.net>

On Jan 28, 12:16 pm, skunkwerk <skunkw... at gmail.com> wrote: > Hi, > I'm trying to find the roots of a logarithmic equation that I've plot ted successfully (I can see both roots are between 0 and 1). > > expr = 7500*x*(1 - x) + 325*8.314*(x*Log[x] + (1 - x)*Log[(1 - x)]) > FindRoot[expr == 0, {x, 0, 1}] > > FindRoot:nlnum: the function value(indeterminate) is not a list of number s with dimensions {1} at {x} = {0.} > > any ideas? > > thanks The problem is most probably the starting value for x: In[18]:= expr /. x -> 0 Limit[expr, x -> 0] During evaluation of In[18]:= Infinity::indet: Indeterminate expression 0 (-\[Infinity]) encountered. >> Out[18]= Indeterminate Out[19]= 0. So, changing the initial value for x, gives a nice result: In[14]:= FindRoot[expr == 0, {x, 0.4}] FindRoot[expr == 0, {x, 0.6}] Out[14]= {x -> 0.468458} Out[15]= {x -> 0.531542} I hope this helped!