solving simple first order condition

*To*: mathgroup at smc.vnet.net*Subject*: [mg54050] solving simple first order condition*From*: juejung <juejung at indiana.edu>*Date*: Wed, 9 Feb 2005 09:27:22 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi all, I have the following problem with a simple First Order Condition (FOC) out of an OLG model in Economics. u[c_] := c^(1 - sigma)/(1 - sigma); Ts[x_] := theta*x; maxFun[se_] := u[(1 - tau)*w - s] + beta*u[R*s + Ts[R*s]]; der = FullSimplify[D[maxFun[s], s]] sol = Solve[{der == 0}, {s}] Why can't Mathematica solve this simple FOC when I can do it so easily by hand. If I use the FOC and replace the (1+theta) by Theta (capital theta) and do the same Solve command, then it works (as shown in sol1 below) and I can get a closed form solution. sol1 = Solve[{(beta*R*Theta)/(R*s*Theta)^sigma - (-s + w - tau*w)^(-sigma) == 0}, {s}] I find it annoying that I apparently have to replace all (1+something) expressions by a single variable (easy here, but cumbersome in more involved models). Is there an easy simplify command hidden somewhere?? Best Juergen ------------------ Juergen Jung Indiana University Bloomington, US -- Using Opera's revolutionary e-mail client: http://www.opera.com/m2/