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If I define a piecewise function

f[t_] := Piecewise[{{t^2, t < 0}, {Sin[t], t > 0}}]
Which[f[t], t > 0]

how do I display only one part of the function? e.g. I want to know what f is when t>0, how do I get Mathematica to output Sin[t]?

(This is a MWE. My actual piecewise function contains thousands of terms when t<0, and I only want to study the function at t>0.)

Edit: Thanks for the responses. I should add that the piecewise function is the solution to a Convolve operation. So I'm not sure if the piecewise function is a "Mathematica function" in the strict sense.

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  • $\begingroup$ What else could it be if it's not a "Mathematica function in the strict sense"? $\endgroup$
    – Roman
    Jun 7, 2019 at 12:04
  • $\begingroup$ I don't know, I'm a Mathematica newbie. What I mean is, it's a function that isn't expressed as f[t_] :=. Instead it's f = . Does this make sense? $\endgroup$
    – Medulla Oblongata
    Jun 7, 2019 at 12:22
  • $\begingroup$ No, it doesn't make sense. Please read a tutorial on immediate and delayed definitions. Both are functions. $\endgroup$
    – Roman
    Jun 7, 2019 at 13:11

2 Answers 2

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PiecewiseExpand[f[t], t > 0]
(*    Sin[t]    *)
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Simplify gives the desired result:

Simplify[f[t], t > 0]

Sin[t]

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