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For those who do not know, the split-complex numbers are an analogue to the complex numbers where J is defined such that $J^2=1$ but $J\ne\pm1$, so they are all of the form $a+bJ$.

By using TagSetDelayed, I tried to define the split-complex numbers as so:

J /: J^2 := 1

If I then type J^2, I get the output 1. However, if I type J^3, I just get the output J^3. I would like to instead get the output $J$, since $J^3=J^2J=1J=J$. Is there a better way to implement this number system?

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    $\begingroup$ Might be easier to do this using 2x2 matrix representations. $\endgroup$ Commented Jan 22, 2019 at 22:28
  • $\begingroup$ Ummmm.... isn't $J = -1$? $\endgroup$ Commented Jan 22, 2019 at 23:28
  • $\begingroup$ Sorry, I forgot to specify that $J\ne -1$ either, I've edited the question to fix that $\endgroup$
    – volcanrb
    Commented Jan 22, 2019 at 23:46

3 Answers 3

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Try this:

J /: Power[J, p_Integer?OddQ] := J
J /: Power[J, p_Integer?EvenQ] := 1


J^Range[-10, 10]

{1, J, 1, J, 1, J, 1, J, 1, J, 1, J, 1, J, 1, J, 1, J, 1, J, 1}

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  • $\begingroup$ This will not work with most functions. See my answer. $\endgroup$
    – Anixx
    Commented Dec 12, 2021 at 14:48
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You can represent split-complex numbers as multivectors (geometric number, clifford number) with signature $(1, 0)$. I have a paclet for this:

PacletInstall["https://wolfr.am/OkONsyY2"]

<< GeometricAlgebra`

(* this is your split-complex number *)
h = Multivector[{a, b}, 1]

(* you can perform numeric operations with it *)
h^2
h^-1
MultivectorFunction[Exp, h] (* similar to MatrixFunction *)
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  • $\begingroup$ See my much simpler answer. $\endgroup$
    – Anixx
    Commented Dec 12, 2021 at 10:22
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This way, add this line to the top of the notebook:

$Post = #/.J->{-1,1}/.{x_,y_}->(x+y)/2+J(y-x)/2&;

Use like this:

In:= Log[J]

Out:= (I Pi)/2 - (I Pi J)/2

In:= I^J

Out:= I J
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