Re: Why do parentheses spuriously appear when I type in a formula?
- To: mathgroup at smc.vnet.net
- Subject: [mg34549] Re: [mg34410] Why do parentheses spuriously appear when I type in a formula?
- From: "Carl K. Woll" <carlw at u.washington.edu>
- Date: Mon, 27 May 2002 01:16:49 -0400 (EDT)
- References: <933FF20B19D8D411A3AB0006295069B0286B1B@debis.com>
- Sender: owner-wri-mathgroup at wolfram.com
DrBob and Hartmut, Since I started this thread, let me add a few words of comment. DrBob compares (the b subscript of T) raised to the a power the b subscript of (T raised to the a power) and states that parentheses are needed in one of the two to be able to distinguish between them. However, the syntax of Mathematica for subscripts is the same as the syntax for superscripts (or power), so this comparison has no relevance to Mathematica. That is, subscripting is given by Subscript[T,b] not Subscript[b,T]. In words, you should compare (T with b subscript) raised to the a power T with (b subscript raised to the a power) if you want to talk about parentheses as related to Mathematica. Now, the question is if parentheses are needed to visually distinguish between these two cases, and the answer is no! There is a clear visual difference between the two. Just compare Superscript[Subscript[T,b],a] Subscript[T,Superscript[b,a]] after deleting the parentheses that show up in the first case. Since there is a clear visual difference between the two, the added parentheses are really just optional, and I would prefer the option without parentheses. Moreover, the designers of Mathematica apparently agreed that the parentheses were really optional. Consider the case with Superscript and Subscript switched. Subscript[Superscript[T,b],a] Superscript[T,Subscript[b,a]] Again the visual difference between the two is clear, but notice that in this case Mathematica does NOT add any parentheses. So the designers of Mathematica decided that in one case they would add parentheses and not in the other. This choice is obviously influenced by the fact that superscripts are usually interpreted as power. At any rate, when I asked my original question, I was looking for a way to make Mathematica NOT add these parentheses. Since the parentheses are added during the input phase (even with no kernel present) adding rules to MakeExpression will not solve the problem. It is possible that modifying one of the text resources might change this behaviour, but I couldn't figure out which file to modify. For example, the file MathMLPatterns seems to be relevant. However, there may be no way for a user to change this behavior. On another note, there is another example where Mathematica adds parentheses, and most people would consider these parentheses to be almost mandatory. This example occurs when you take the subscript or superscript of a quotient. So, it is important that Mathematica be able to add parentheses when necessary for visual reasons. Still, as Hartmut points out, there is never any ambiguity in what is meant when one uses one dimensional input, since everything has a precedence. The expression without parentheses may not be what you want, but that doesn't mean the expression is ambiguous. The only time there is any ambiguity is when this one dimensional input is converted to two dimensional (visual) form. Also, Hartmut asks whether I could use Ctrl^% to get my input, and the answer is no. I was trying to come up with a way to input tensors, and for tensors the order of indices is important. Using Ctrl^% loses the information about which index comes first. Carl Woll Physics Dept U of Washington "DrBob" <majort at cox-internet.com> wrote in message news:ackolu$8f8$1 at smc.vnet.net... > >>the b subscript of T raised to the a power > > I read that wrong before. Sorry. > > If you mean (the b subscript of T) raised to the a power, the keystrokes > are T Ctrl-_ b Ctrl-space Ctrl-^ a, and there are no parentheses. > > If you mean the b subscript of (T raised to the a power), the keystrokes > are T Ctrl-^ a Ctrl-space Ctrl-_ b, and there MUST be parentheses in > order to distinguish between that and the other answer. If you care. > If you don't, then use the other method and avoid the parentheses. > > I see no other reasonable way to read it, and I see no reliable way to > visually distinguish between the two forms without parentheses in one of > them. > > >>You can also check the input which does work: first the subscript, > then the subscript; the ctrl-space escape *is* needed! > > That's obviously a typo... so I still haven't seen the answer you DO > want. > > Bobby > > -----Original Message----- > From: Wolf, Hartmut [mailto:Hartmut.Wolf at t-systems.com] To: mathgroup at smc.vnet.net > Subject: [mg34549] RE: Why do parentheses spuriously > appear when I type in a formula? > > > > -----Original Message----- > > From: DrBob [mailto:majort at cox-internet.com] To: mathgroup at smc.vnet.net > > Sent: Thursday, May 23, 2002 5:01 PM > > Subject: [mg34549] RE: Why do parentheses spuriously > > appear when I type in a formula? > > > > > > >>My exact key strokes are T Ctrl-^ a Ctrl-space Ctrl-_ b. > > > > Omit "Ctrl-space" and you get what you want. > > [Hartmut Wolf] No, Bobby, this gives something different: mark the box, > Menu > Format > Show Expression to see > > Cell[BoxData[ > SuperscriptBox["T", > SubscriptBox["a", "b"]]], "Input"] > > which was *not* wanted, see also Out[2] of my first reply. You can also > check the input which does work: first the subscript, then the > subscript; > the ctrl-space escape *is* needed! > > Quite obviously there is a bug at forming the input stream (or rather > it's > display in StandardForm). Comparing Out[13] with Out[3] (of my first > reply) > shows what: instead of invisible brackets \(...\) visible ones (...) are > interspersed at box formation around T\^a at the very moment when ctr-_ > is > pressed. > > I tried adding a semantic rule to the parser (expression formation) > > In[3]:= > MakeExpression[SubscriptBox[RowBox[{"(", SuperscriptBox[T_, a_], ")"}], > b_], > > StandardForm] := > MakeExpression[SubscriptBox[SuperscriptBox[T, a], b], StandardForm] > > but it doesn't trigger (or shouldn't?, or couldn't because this is no > issue > of expression formation? already too late? I'd like to know!) > > Trying InputForm... > > In[6]:= \!\(\((T\^a)\)\_b // InputForm\) > Out[6]//InputForm= Subscript[T^a, b] > > In[7]:= \!\(\(T\^a\)\_b // InputForm\) > Out[7]//InputForm= Subscript[T^a, b] > > ...shows that both forms, with and without explicit parentheses, convert > to > the same InputForm (i.e. same expression). However doing it in reverse > > In[8]:= Subscript[T^a,b]//StandardForm > Out[8]//StandardForm= \!\(\((T\^a)\)\_b\) > > brings up again the unwanted parentheses. Perhaps for calculation just > don't > bother with them, but if you finally want to show something printable > for > publication, the spurious parentheses are disturbing and more than ugly! > > -- > Hartmut > > > > > > Bobby Treat > > > > -----Original Message----- > > From: Wolf, Hartmut [mailto:Hartmut.Wolf at t-systems.com] To: mathgroup at smc.vnet.net > > Sent: Wednesday, May 22, 2002 1:46 AM > > Subject: [mg34549] Why do parentheses spuriously appear > > when I type in a formula? > > > > > -----Original Message----- > > > From: Carl K. Woll [mailto:carlw at u.washington.edu] To: mathgroup at smc.vnet.net > > > Sent: Saturday, May 18, 2002 9:52 AM > > > Subject: [mg34549] Why do parentheses spuriously > > appear when > > > > > I type in a > > > formula? > > > > > > > > > Hi all, > > > > > > For some strange reason, I want to type into Mathematica an > > > expression that > > > should look like T^a_b, that is, the b subscript of T raised > > > to the a power. > > > My exact key strokes are T Ctrl-^ a Ctrl-space Ctrl-_ b. > > > However, when I > > > enter this expression into mathematica, it adds (spuriously > > > in my mind) some > > > parentheses, so that I get (T^a)_b. I would like to know what > > > causes these > > > parentheses to be added, and if there is anything I can do to > > > prevent them > > > from appearing. What I have to do now is go back into the > > > expression and > > > edit out the parentheses. > > > > > > Carl Woll > > > Physics Dept > > > U of Washington > > > > > > > > > > > > > Dear Carl, > > > > of course as to the why, I could at most speculate. I > > wouldn't do that, > > instead just add an observation: > > > > If we input "T Ctrl-^ a Ctrl-space Ctrl-_ b" as you described, we get > > > > Cell[BoxData[ > > SubscriptBox[ > > RowBox[{"(", > > SuperscriptBox["T", "a"], ")"}], "b"]], "Input"] > > > > What you desired however is this: > > > > Cell[BoxData[ > > SubscriptBox[ > > SuperscriptBox["T", "a"], "b"]], "Input"] > > > > If I try one-dimensional input, to reach that I must add a bracket \( > > ... \) > > > > In[13]:= \(\(T\^a\)\_b\) > > Out[13]= SubscriptBox[SuperscriptBox[T,a],b] > > > > otherwise I'd get something different and unwanted > > > > In[2]:= \(T\^a\_b\) > > Out[2]= SuperscriptBox[T,SubscriptBox[a,b]] > > > > Parenthesis as from your undesired behaviour are reproduced with > > > > In[3]:= \((T\^a)\_b\) > > Out[3]= SubscriptBox[RowBox[{(,SuperscriptBox[T,a],)}],b] > > > > (without the backslashes!) In contrast the complementary T can be > > reached by > > "T ctrl-_ a ctrl-blank ctrl-^ b" > > > > Cell[BoxData[ > > SuperscriptBox[ > > SubscriptBox["T", "a"], "b"]], "Input"] > > > > or simply as > > > > In[5]:= \(T\_a\^b\) > > Out[5]= SuperscriptBox[SubscriptBox[T,a],b] > > > > Related forms are produced as they should: > > > > In[23]:= \(T\_\(a\^b\)\) > > Out[23]= SubscriptBox[T,SuperscriptBox[a,b]] > > > > In[25]:= \(T\^\(a\_b\)\) > > Out[25]= SuperscriptBox[T,SubscriptBox[a,b]] > > > > > > If you want to input fluently, perhaps it helps to first enter the > > subscription: > > "T ctl-_ b arrowleft arrowleft ctrl-^ a end" > > > > Perhaps you can use the form > > > > In[29]:= \(T\^a\%b\)//DisplayForm > > Out[29]//DisplayForm= > > \!\(\* TagBox[\(T\_b\%a\), DisplayForm]\) > > > > which inputs straight foreword as "T ctrl-^ a ctrl-% b" > > > > Cell[BoxData[ > > SubsuperscriptBox["T", "b", "a"]], "Input"] > > > > -- > > Hartmut > > > > > > > > > > >