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Re: Query about using FindRoot on function defined via Module

• To: mathgroup at smc.vnet.net
• Subject: [mg102856] Re: Query about using FindRoot on function defined via Module
• From: Harutyun Amirjanyan <amirjanyan at gmail.com>
• Date: Sat, 29 Aug 2009 06:34:12 -0400 (EDT)
• References: <h77n8k$s1h$1@smc.vnet.net>

As you can find in help FindRoot (like Plot) first localizes the
values of all variables, then evaluates f with the variables being
symbolic, and then repeatedly evaluates the result numerically.

to prevent this you can use Evaluated -> False option
(this somewhy isn't documented. see http://web.ift.uib.no/~szhorvat/mmatricks.php)

F[x_] := Module[{t}, NIntegrate[t, {t, 0, x}] - 2]
FindRoot[F[x], {x, 0.2}, Evaluated -> False]

or define your function only for numbers

F1[x_?NumberQ] := Module[{t}, NIntegrate[t, {t, 0, x}] - 2]
FindRoot[F1[x], {x, 0.2}]