FindRoot and Interpolating function

• To: mathgroup at smc.vnet.net
• Subject: [mg80273] FindRoot and Interpolating function
• From: vmany <veeramany.arun at gmail.com>
• Date: Thu, 16 Aug 2007 04:48:10 -0400 (EDT)

```FindRoot[S[a[1]] == 0.0018, {a[1], 50}]

where S[a[1]] below contains an interpolating function.

\!\(\*
RowBox[{\(0.00001799999999999999`\ \[ExponentialE]\^\(1\/4\ \((50 -
a[1])\)\
\)\), "+",
FractionBox[
RowBox[{"0.09999999999999998`", " ", \(\[ExponentialE]\^\(\
(-0.25`\)\ a[
1.`]\)\), " ", \((\(-50.`\) + a[1])\), " ",
RowBox[{"(",
RowBox[{\(\(1216.24812344918`\)\(\[InvisibleSpace]\)\),
"+",
RowBox[{\(\[ExponentialE]\^\(0.25`\ a[1.`]\)\), " ",
RowBox[{
TagBox[\(InterpolatingFunction[{{0.`, 89.`}}, "<>"]\),
False,
Editable->False],
"[", \(\(\(0.`\)\(\[InvisibleSpace]\)\) + a[1.`]\),
"]"}]}]}], ")"}]}], \(\(-50.`\) + a[1.`]\)]}]\)

FindRoot gives the following error:
FindRoot::nlnum: The function value ...is not a list of numbers with
dimensions {1} at {a[1]} = {55.}

How do I deal with this?

Many thanks
Arun

```

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