Cfrgtkky

I'd like to get the appended below commutative diagram by using tikz-cd. The source has been made in TeX, and the positioning of the nodes at the bottom row i.e. coker ker f and ker coker f have been obtained by the macro hidewidth. But how can I get a similar result of hidewidth in tikzcd?

The code in tikz-cd, without the alignment I'd like to get, is the following:

begin{center}

begin{tikzcd}

    ker f arrow[r,"varepsilon"] & A arrow[r,"f"] arrow[d] & Barrow[r,"pi"] & coker f \

    & cokerker farrow[r,dotted,"bar f"] & kercoker farrow[u]

end{tikzcd}

end{center}

Thank you!

Maybe not a perfect solution, but it is starting point.

documentclass{report}

usepackage{amsthm,amsmath,amssymb,amsfonts}

usepackage{tikz-cd}



begin{document}

[

begin{tikzcd}

operatorname{Ker} f arrow[r] & A arrow[r]arrow[d] & B arrow[r] & operatorname{Coker} f \

& llap{$operatorname{Coker} operatorname{Ker}{}$}f arrow[r] & mathrm{K} rlap{$operatorname{er}operatorname{Coker} f $}arrow[u]

end{tikzcd}

]

end{document}

A variant based on mathllap and mathrlap from mathtools; and a simple makebox:

documentclass{report}

usepackage{mathtools,amssymb}

usepackage{tikz-cd}

usepackage{calc} 

DeclareMathOperator{Ker}{Ker}

DeclareMathOperator{Coker}{Coker}



begin{document}



[

begin{tikzcd}

Ker f arrow[r] & A arrow[r]arrow[d] & B arrow[r] & Coker f \

& mathllap{Coker Ker{}} f arrow[r] & makebox[widthof{$B$}][l] {$mathrlap{KerCoker f}$}arrow[u]

end{tikzcd}

]



end{document}

A pure tikz-cd solution, without hacking with makebox, mathllap, llap or similar.

You can use the option:

/tikz/column 2/.append style={nodes={anchor=base east}}

to right align the nodes of the second column and:

/tikz/column 3/.append style={nodes={anchor=base west}}

to left align the nodes of the second column.

Then you can use the option to path to indicate the path you need, for example to path={-- (tikztostart |- tikztotarget.north)}] means "go to the point which has the x coordinate of the starting point and the y coordinate of the endpoint, north anchor.

For the arrow from the bottom left node to B, I used <- to invert the direction of the arrow in order to start it from B and being able to use to path.

I've also used &[-5em] to reduce the space between the first and the second column and between the third and the last.

documentclass{report}

usepackage{amsthm,amsmath,amssymb,amsfonts}

usepackage{tikz-cd}



begin{document}

[

begin{tikzcd}[%

    /tikz/column 2/.append style={nodes={anchor=base east}},

    /tikz/column 3/.append style={nodes={anchor=base west}}

    ]

operatorname{Ker} f arrow[r] &[-5em] A arrow[r]arrow[d, start anchor=south,to path={-- (tikztostart |- tikztotarget.north)}] & B arrow[r]arrow[d, <-,to path={-- (tikztostart |- tikztotarget.north)}] &[-5em] operatorname{Coker} f \

& operatorname{Coker} operatorname{Ker} f arrow[r] & operatorname{Ker} operatorname{Coker} f 

end{tikzcd}

]

end{document}

To be honest I'd prefer the top one. Anyway, this case can be solved by simply assign a fixed width to the long objects, here 1em, making them stick to the left and to the right respectively.

documentclass{article}

usepackage{amsmath}

usepackage{tikz-cd}



DeclareMathOperator{coker}{coker}



begin{document}



[% not center

begin{tikzcd}

ker f arrow[r,"varepsilon"] &

A arrow[r,"f"] arrow[d] &

Barrow[r,"pi"] & coker f

\

&

cokerker f arrow[r,dashed,"bar f"] &

kercoker f arrow[u]

end{tikzcd}

]



[% not center

begin{tikzcd}

ker f arrow[r,"varepsilon"] &

A arrow[r,"f"] arrow[d] &

Barrow[r,"pi"] & coker f

\

&

makebox[1em][r]{$cokerker f$} arrow[r,dashed,"bar f"] &

makebox[1em][l]{$kercoker f$} arrow[u]

end{tikzcd}

]



end{document}

Why not center? Because with [...] the display will not be separated by the text above it (no blank line before [).

If you prefer “Ker” and “Coker” with the capital letter, use DeclareMathOperator as shown for defining Ker and Coker.