Re: cannot work a "conditional If"

• To: mathgroup at smc.vnet.net
• Subject: [mg130572] Re: cannot work a "conditional If"
• From: Peter Pein <petsie at dordos.net>
• Date: Tue, 23 Apr 2013 00:02:24 -0400 (EDT)
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```Am 22.04.2013 09:13, schrieb patrice.haldemann at gmail.com:
> Hi everybody
>
> I am a newcomer in the mathematica world and I have been facing an issue for some days.
>
> I have used mathematica to solve an NDSolve and it has worked well
>
> I have tested  expressions with the solution of NDSolve and its has worked well.
>
> Now if I use an expression in an "Conditional If", it does not work.
>
> Thank you for your help
>
>
> See below
>
> signy[t_] := y[t] /. orbit   where y[t] is the solution of the NDSolve
>
> signy[1]
>
> {-1.96861}
>
>  ang12[t_] := If[signy[t] > 3, 10, 6]
>
>  ang12[1]
>
> If[{-1.96861} > 3, 10, 6]
>
>
>
>

Hi Patrice,

You might have noticed the curly braces around the computed value.
Your function signy returns a list with one element, not a value.

signy[t_] := y[t] /. First[orbit]

should work.

Peter

```

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