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Topic: cannot work a "conditional If"
Replies: 1   Last Post: Apr 24, 2013 6:16 AM

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Bob Hanlon

Posts: 906
Registered: 10/29/11
Re: cannot work a "conditional If"
Posted: Apr 24, 2013 6:16 AM
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Your output of signy is a list of length 1 rather than a number.
Consequently, the test in the If does not evaluate as either True or False
and the If statement returns unevaluated. Change the definition of signy to
produce a number, i.e.,

signy[t_] := y[t] /. orbit[[1]]

However, rather than use an If statement, I recommend that you use

Bob Hanlon

On Mon, Apr 22, 2013 at 3:11 AM, <> wrote:

> 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]

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