Returning Sin[t] from package turns into Sin[scope`t] [duplicate]

Question

I have a function in scope that returns an expression with a variable t

BeginPackage["Pkg`"]
F1::usage = "";
Begin["scope`"]
F1[x_] := Sin[t + x];
End[]
EndPackage[]

When I use it from outside

In[159]:= F1[2]
Out[159]= Sin[2 + scope`t]

I can Replace scopettot` outside

In[169]:= F1[2] /. scope`t -> t
Out[169]= Sin[2 + t]

But is there any way to replace it from the inside of Package ?

I have tried replacing t with "t"

BeginPackage["Pkg`"]
F1::usage = "";
Begin["scope`"]
F1[x_] := Sin[t + x] /. t -> "t";
End[]
EndPackage[]

This looks like it works

In[223]:= F1[2]
Out[223]= Sin[2 + t]

However it is actually Sin[2 + "t"] So I cannot plot it with variable t

Plot[F1[2], {t, 0, 200}]

doesn't plot anything

You need to define t as a public variable as well as F1, with a usage message in the same way. — SPPearce, Commented Nov 11, 2016 at 13:02
@KraZug You should write your comment up as an answer, it seems like the most elegant solution & helped me out with a similar problem. — Chris K, Commented Nov 11, 2016 at 19:45
@Chris The reason I didn't was because I assumed that the question would get closed. — SPPearce, Commented Nov 11, 2016 at 19:51

user21 · Accepted Answer · 2016-11-11 14:40:56Z

3

t needs to be an argument of your function F1 like so:

BeginPackage["Pkg`"]
F1::usage = "";
Begin["scope`"]
F1[x_, t_] := Sin[t + x];
End[]
EndPackage[]

The calling it:

F1[x, t]
(*Sin[t + x]*)

answered Nov 11, 2016 at 14:40

user21

40.7k8 gold badges114 silver badges170 bronze badges

$\begingroup$ Is there any way to force t to be a variable not a value so that it doesn't conflict with a global variable t declared in user's notebook ? $\endgroup$
– Neel Basu
Commented Nov 12, 2016 at 18:57
$\begingroup$ @NeelBasu, I don't understand what you are looking for. Can you show (code) what is conflicting in this case? $\endgroup$
– user21
Commented Nov 12, 2016 at 19:37
$\begingroup$ If I have t=42 in my Notebook prior invoking F1[x, t] it will use that t and return Sin[x + 42]. So is there any way such that user is forced to pass a variable only. or the symbol is used instead of its value even if a predefined variable is passed. $\endgroup$
– Neel Basu
Commented Nov 13, 2016 at 13:41
$\begingroup$ Use something like 't_Symbol' in the definition of F1. Have look in the documentation under pattern matching. $\endgroup$
– user21
Commented Nov 13, 2016 at 20:51

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SPPearce · Accepted Answer · 2016-11-11 19:55:50Z

2

Simply add a usage definition the variable t as well as F1 (and in general, anything you want to return from your package)

BeginPackage["Pkg`"]
F1::usage = "";
t::usage = "time variable";
Begin["scope`"]
F1[x_] := Sin[t + x];
End[]
EndPackage[]

Then the t that is returned works fine.

answered Nov 11, 2016 at 19:55

SPPearce

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$\begingroup$ If the user code uses a variable t it use that instead $\endgroup$
– Neel Basu
Commented Nov 12, 2016 at 18:50
$\begingroup$ This code does not work when there is a global definition for t. E.g. try t=1 and then run your code. $\endgroup$
– user21
Commented Nov 12, 2016 at 19:35

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2 Answers 2