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I got the following output of FullSimplify, when expecting to get "0".

output

I found no explanation of this output here. Could you please explain, what it means? That my expression equals zero when the condition $m^4 \Omega ^2 \sin ^2(\theta )+2 m r<r^2$ holds and that big fraction otherwise? Or maybe something else?

J. M.'s missing motivation
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  • Duplicate of https://mathematica.stackexchange.com/q/102259/12 In that post, also look at the linked questions on the right. – Szabolcs Oct 24 '17 at 12:23
  • @Szabolcs not necessarily. Perhaps Piecewise in general was unknown to OP. – LLlAMnYP Oct 24 '17 at 14:46
  • @LLlAMnYP This has been asked several times before. There are many practically identical questions marked as a duplicate of that one (which is why I said look at the sidebar). I agree that the answer there needs a slight updating to accommodate these better. It can't me marked as a duplicate of a post that is already closed as a duplicate. – Szabolcs Oct 24 '17 at 14:53
  • @Szabolcs sorry, didn't read the last half of your comment \_('')_/ – LLlAMnYP Oct 24 '17 at 14:54
  • @Szabolcs well I've looked through the questions, and if anything is a duplicate, it's this one: https://mathematica.stackexchange.com/q/109071/26956 But I reckon the suggestion to inspect the FullForm when encountering an output you don't understand is more general. Not sure if vote to leave open or nominate this link as another duplicate. – LLlAMnYP Oct 24 '17 at 15:03
  • @LLlAMnYP reopened – Kuba Oct 25 '17 at 07:04

1 Answers1

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my expression equals zero when the condition m4Ω2sin2(θ)+2mr<r2 holds and that big fraction otherwise?

Your assumption is correct. What you see is the typeset OutputForm of Piecewise.

Normally you can simply highlight an expression or a keyword, hit F1 and see the documentation page for it, but in this case it doesn't seem to work, so it's understandably unclear.

What you can do, however, is to run FullForm@% after you get a result like that. The output will be something like

Piecewise[ (* stuff *) ]

then you can realize that you need to look up Piecewise.

LLlAMnYP
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