Re: How to NSolve equation which involves NIntegrate?

*To*: mathgroup at smc.vnet.net*Subject*: [mg120084] Re: How to NSolve equation which involves NIntegrate?*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Fri, 8 Jul 2011 04:50:50 -0400 (EDT)*References*: <201106250929.FAA20235@smc.vnet.net>*Reply-to*: drmajorbob at yahoo.com

Clear[f, g] f[a_?NumericQ] := NIntegrate[Sin[a x], {x, 0, 1}] g[a_] := a*a FindRoot[f[a] - g[a], {a, 1}] {a -> 0.490073} a) NumericQ eliminates the error you mentioned, b) NSolve is limited to algebraic problems, and c) I had to come up with a starting point for the search. (a) and (b) are related, in that NSolve wanted to keep a symbolic in solving the problem, but f[a] is undefined, when a is symbolic. Bobby On Thu, 07 Jul 2011 09:58:23 -0500, Ted Sariyski <tsariysk at craft-tech.com> wrote: > I am sorry, I should made up an example. Here it is: > > f[a_] := NIntegrate[Sin[a x], {x, 0, 1}] > g[a_] := a*a > NSolve[f[a] == g[a], a] > > Out[]: NIntegrate::inumr: "The integrand Sin[a x] has evaluated to > non-numerical values for all sampling points in the region with > boundaries {{0,1}}." > > Thanks, > --Ted > > On 7/7/2011 10:26 AM, DrMajorBob wrote: >> You left out the definition of h, so how can we possibly tell you why >> it evaluates to non-numerical values? >> >> Bobby >> >> On Thu, 07 Jul 2011 06:31:38 -0500, Ted Sariyski >> <tsariysk at craft-tech.com> wrote: >> >>> Hi, >>> I need a numerical solution for a system of equations which involve >>> numerical integrals. For one parameter the equation would be: >>> >>> f[a]==g[a] >>> where >>> f[a_]:=NIntegrate[h[x, a] , {x, x1, x2}] >>> >>> NSolve returns: "The integrand has evaluated to non-numerical values". >>> >>> Is there a built-in procedures for this type of problems or I need to >>> make explicit iterations? >>> >>> Thanks in advance, >>> --Ted >>> >>> >>> >>> >>> >> >> > -- DrMajorBob at yahoo.com