# Hiding arrow in xymatrix?

I want to enlarge a xy-diagram. Using the \invisible command, I got some strange spacing. That's why I decided to redraw the complete diagram using the \only and the \phantom command. But there is an arrow, which does not react on \phantom and which I need for correct spacing.

In my picture it is the arrow with label \Psi. How can I hide it?

Here is my - not so minimal - example:

\documentclass{beamer}
\usetheme{Copenhagen}
%Packages
\usepackage{amsmath}
\usepackage{amssymb,bbm,amsthm}
\usepackage[ngerman]{babel}
\usepackage[all,knot,color]{xy}
\xyoption{arc}
%Some personal commands, that should not matter
\newcommand{\C}{\mathbbm{C}}
\renewcommand{\H}{\mathbbm{H}}
\newcommand{\Exp}{\operatorname{Exp}}
\newcommand{\QL}[2]
{{\left.\raisebox{-.1em}{\ensuremath{#1}}\middle\backslash\raisebox{.1em}{\ensuremath{#2}}\right.}}
% Arrow for a bijective mapping
\newcommand{\bijar}[1][]{%
\ar[#1]
\ar@<0.4ex>@{}[#1]|-*=0[@]{\sim}}
\let\varpi\pi
\newcommand{\ggruppe}{{<\!\! g \!\! >}}
\begin{document}
\begin{frame}
\only<1>{$\xymatrix@R=13pt@C=12pt{ \H\times\C \ar @{>>} [rr]^{\Exp} \ar @{>>} [rd]_{\varpi_1} \ar @{>>}[dd]_{\varepsilon_N}& & D^\times\times\C^\times \\ & \QL{G_1}{\H\times\C} \ar @{>>}[dl]^{\varepsilon_{N,1}} \bijar [ur]_-{\Phi_1}& & {\phantom{\QL{\ggruppe}{D^\times\times\C^\times}}} \ar @/^5pc/ @{-->>} [dlll]^{\Psi} \\ E^0(N) & & {\phantom{\QL{G_2}{\H\times\C}}} }$}
\only<2>{$\xymatrix@R=13pt@C=12pt{ \H\times\C \ar @{>>} [rr]^{\Exp} \ar @{>>} [rd]_{\varpi_1} \ar @{>>}[dd]_{\varepsilon_N}& & D^\times\times\C^\times \ar @{>>} [dr]_-{p_g} \\ & \QL{G_1}{\H\times\C} \ar @{>>}[dl]^{\varepsilon_{N,1}} \ar @{>>} [dr]_{\varpi_2} \bijar [ur]_-{\Phi_1}& & \QL{\ggruppe}{D^\times\times\C^\times} \ar @/^5pc/ @{-->>} [dlll]^{\Psi} \\ E^0(N) & & \QL{G_2}{\H\times\C} \ar @{>>} [ll]^{\varepsilon_{N,2}} \bijar [ur]_{\Phi_2} }$}
\end{frame}
\end{document}

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I'm reading your diagram. Why are you using the command \QL with raisebox? It's so ugly. – Sigur Apr 30 '13 at 22:52
@Sigur: Actually, I kind of like the effect that Greyfox achieves here for taking quotients on the left. Normally, when I see something typeset like G \ H x C, I find it confusing to translate this to "take H x C and mod out by G acting on the right." When something like this is handwritten, the G is often lowered slightly to emphasize that the "main noun of the noun phrase" is H x C. – Charles Staats May 2 '13 at 12:49
@CharlesStaats This is exactly the idea of the raiseboxes. I just want to add, that it avoids a lot of brackets, since one should write G \ (H x C) for beeing exact - I usually have (G x Z)(H x C). Also I have a few double qoutients, e.g. I show that C(B\A) and (C\B)\A are isomorphic. When A,B,C are products I find it easier to read, if I have a fraction-like quotient. – Greyfox May 2 '13 at 18:15

I changed a little bit. For example, I inserted the \sim for bijection directly on the arrow.

Is it necessary to use that raise box for some commands? Also, why not use \langle \rangle instead of < >?

\begin{frame}[t] %% note the option [t] here
\only<1>{$\xymatrix@R=13pt@C=12pt{ \H\times\C \ar @{->>}[rr]^{\Exp} \ar@{->>}[rd]_{\varpi_1}\ar@{->>}[dd]_{\varepsilon_N} & & D^\times\times\C^\times \ar@{->>}[dr]_-{p_g} \\ & \QL{G_1}{\H\times\C}\ar@{->>}[dl]^{\varepsilon_{N,1}} \ar[ur]_-{\Phi_1}^{\sim}\ar[dr]_{\pi_2} & & \QL{\ggruppe}{D^\times\times\C^\times} \\ E^0(N) & & \QL{G_2}{\H\times\C} \ar@{->>}[ll]^{\varepsilon_{N,2}} \ar[ur]_{\Phi_2}^{\sim} }$}

\only<2->{$%% I changed the overlay specification here \xymatrix@R=13pt@C=12pt{ \H\times\C \ar @{->>}[rr]^{\Exp} \ar@{->>}[rd]_{\varpi_1}\ar@{->>}[dd]_{\varepsilon_N} & & D^\times\times\C^\times \ar@{->>}[dr]_-{p_g} \\ & \QL{G_1}{\H\times\C}\ar@{->>}[dl]^{\varepsilon_{N,1}} \ar[ur]_-{\Phi_1}^{\sim}\ar[dr]_{\pi_2} & & \QL{\ggruppe}{D^\times\times\C^\times} \ar @/^5pc/ @{-->>} [dlll]^{\Psi} \\ E^0(N) & & \QL{G_2}{\H\times\C} \ar@{->>}[ll]^{\varepsilon_{N,2}} \ar[ur]_{\Phi_2}^{\sim} }$}

\only<3->{text to appear starting from 3rd slide}
\end{frame}


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As far as I see, you just left the arrow away in the first diagram. As a result the diagram needs less space. When I add the arrow in the second diagram, LaTeX moves the position a bit, especialy if I have text above the diagram. I search for a way to "phantomise" the arrow first, so that the first part of the diagram stays exactly, where it is and the second part just appears later. I tried \phantom{\ar ...}, but without any success. – Greyfox May 1 '13 at 17:08
Thx for the advice of using \langle. When I found out about these commands I changed them nearly everywhere in my files. Obviously I forgot here. – Greyfox May 1 '13 at 17:10
@Greyfox, yes, you are right. I had noticed that. In this case, I suggest you to use a frame only for the diagram and use an option to vertical align on the top, that is, \begin{frame}[t]. – Sigur May 2 '13 at 12:28
@Greyfox, please, see the edited code above. – Sigur May 2 '13 at 12:32
Now, I understand and I can do, as you wrote. Actually in my case, there is text above the diagram. But your solution should still work, I think. Until now, I solved the problem in an ugly way, by adding a vspace below the diagram, which I adjusted by hand. Thx a lot, for your ideas! – Greyfox May 2 '13 at 18:19