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Re: cannot work a "conditional If"
Posted:
Apr 24, 2013 6:16 AM


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 Piecewise.
Bob Hanlon
On Mon, Apr 22, 2013 at 3:11 AM, <patrice.haldemann@gmail.com> 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] > >



