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I implemented this custom notation...

In[57]:= Notation[ParsedBoxWrapper[
RowBox[{"x_", "↓", "y_"}]] ⟺ 
  ParsedBoxWrapper[
RowBox[{" ", 
RowBox[{"FunctionExpand", "[", 
RowBox[{"FactorialPower", "[", 
RowBox[{"x_", ",", "y_"}], "]"}], "]"}]}]]]

and works as expected:

In[71]:= x↓2

Out[71]= (-1 + x) x

What I really want is that when I enter x ^ ( 2 ) that this is interpreted as FactorialPower[x,2] meaning that the outer ( and ) make it a FactorialPower instead of a normal power.

Which changes should I implement to achieve this?

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  • $\begingroup$ Not sure if it is what you are asking, but ctrl-6 on my mac gives a shortcut to raise something to a power. I have to use the arrow keys to move from that to the "normal" line of the equation. The "6" is the up carrot so if you are using a PC, there is probably an equivalent using the key with the up carrot. $\endgroup$ – Mark R Feb 7 '20 at 23:02
  • $\begingroup$ I have windows, I can do that too with ctr-6. If I create 5^(2) I get 25 instead of 20. $\endgroup$ – nilo de roock Feb 8 '20 at 8:08
  • $\begingroup$ @niloderoock I don’t understand what you’re looking for. It isn’t clear what you’re trying to shortcut to what. Can you provide a little more context, maybe what the definition of this shortcut should be? $\endgroup$ – CA Trevillian Feb 9 '20 at 4:21
  • $\begingroup$ Falling should give 5*4*3=60 rising should give 5*6*7=210 $\endgroup$ – CA Trevillian Feb 9 '20 at 4:30
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    $\begingroup$ Mma has the function FactorialPower which handles this. I am mainly concerned about the formatting / notation. - I am now investigating the Notation Package but that is not an easy package. $\endgroup$ – nilo de roock Feb 9 '20 at 8:19
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Another non-Notation option is to use InputAliases:

CurrentValue[EvaluationNotebook[], {InputAliases, "fp"}] = TemplateBox[
    {"\[SelectionPlaceholder]", "\[Placeholder]"},
    "FactorialPower",
    SyntaxForm->SuperscriptBox
]

Then, typing Esc f p Esc will generate the desired input.

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2
  • $\begingroup$ So Notation is not necessary after all. $\endgroup$ – nilo de roock Feb 11 '20 at 13:25
  • $\begingroup$ At the end of the day I want to be able to switch between normal exponents, falling exponents and rising exponents. To start with, I would like ( in "a falling exponents mode" ), x^2-x to display as x^(2). - Could this be the reason why initially Notation was suggested? I hoped the Notation[ _ <=> _] would be able to do this. $\endgroup$ – nilo de roock Feb 11 '20 at 13:42
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This code interprets the superscript (achieved with ctrl+6) as FactorialPower:

MakeExpression[SuperscriptBox[x_, RowBox[{"(", y_, ")"}]], StandardForm] := 
  MakeExpression[RowBox[{FactorialPower, "[", x, ",", y, "]"}], StandardForm]

Then an input of

$a^{(b+c)}$

leads to

FactorialPower[a,b+c]
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  • $\begingroup$ How can I add FunctionExpand after FactorialPower ? I want (x+5)^(3) to evaluate to (x+5)(x+4)(x+3) ; FactorialPower as a name should never appear. $\endgroup$ – nilo de roock Feb 11 '20 at 13:25
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    $\begingroup$ You can add a layer of RowBox[{FunctionExpand,"["...,"]"}] around the FactorialPower inside MakeExpression. $\endgroup$ – QuantumDot Feb 11 '20 at 16:24
  • $\begingroup$ I found it very hard to choose which answer to accept, sorry. $\endgroup$ – nilo de roock Feb 24 '20 at 8:08

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