Re: FindRoot and NIntegrate

*To*: mathgroup at smc.vnet.net*Subject*: [mg81881] Re: FindRoot and NIntegrate*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Sat, 6 Oct 2007 04:28:31 -0400 (EDT)*References*: <fe4tfg$5h$1@smc.vnet.net>

mfedert at gmail.com wrote: > Hi all, > > I have what is probably a very simple problem. I want to find x which > solves an equation of the form > > \integral f(x,y) dy = 0 > > I have tried something along the lines of > > FindRoot[ NIntegrate[ f(x,y) , {y, -inf, inf} ], {x, x_0 } ] > > but it doesn't work ---- my theory being that NIntegrate tries to go > ahead and do the numerical integration before it knows what x is equal > to... which blows up because the integrand is - as a function of x - > non-numerical... Is there a way around this? I'm sure there's some > trivial modification I can make to get things working again. > Here's an example: In[1]:= integral[a_?NumericQ] := NIntegrate[Exp[a*x], {x, 0, 1}] In[2]:= FindRoot[integral[x] == 2, {x, 1}] Out[2]= {x -> 1.2564312086261675} -- Szabolcs