Ytdyklly

What is the best way to create diagrams like these in LaTeX? Is Tikz the way to go?

(Code for these specific instances would be useful but is not absolutely required, since I'll be needing to make diagrams similar in spirit but not identical. Also, this has almost certainly been asked before, so I would equally appreciate a link to a previous asking -- I'm just unsure what terms to search to find such a post.)

edit: looked at some old code and came up with

begin{tikzpicture}



draw[ultra thick,domain=0:1,samples=100, postaction={decorate}, decoration={markings, mark=at position 0.5 with {arrow{stealth}}}] (0,1) -- (0,0);

draw[ultra thick,domain=0:1,samples=100, postaction={decorate}, decoration={markings, mark=at position 0.5 with {arrow{stealth}}}] (1,1) -- (0,1);

draw[ultra thick,domain=0:1,samples=100, postaction={decorate}, decoration={markings, mark=at position 0.5 with {arrow{stealth}}}] (1,0) -- (1,1);

draw[ultra thick,domain=0:1,samples=100, postaction={decorate}, decoration={markings, mark=at position 0.5 with {arrow{stealth}}}] (0,0) -- (1,0);



node at (.5,-.2) {$a$};



end{tikzpicture}

although this seems rather clunky.

Welcome to TeX.SE! This answer makes use of this answer.

documentclass[tikz,border=3.14mm]{standalone}

usetikzlibrary{decorations.markings}



begin{document}

tikzset{lab dis/.store in=LabDis,

lab dis=0.3,

->-/.style args={at #1 with label #2}{decoration={

  markings,

  mark=at position #1 with {arrow{>}; node at (0,LabDis) {#2};}},postaction={decorate}},

  -<-/.style args={at #1 with label #2}{decoration={

  markings,

  mark=at position #1 with {arrow{<}; node at (0,LabDis)

  {#2};}},postaction={decorate}},

 -*-/.style={decoration={

  markings,

  mark=at position #1 with {fill (0,0) circle (1.5pt);}},postaction={decorate}},

  }



begin{tikzpicture}[>=latex]

 draw[->-=at 0.125 with label {$b$},

 ->-=at 0.375 with label {$a$},

 -<-=at 0.625 with label {$b$},

 -<-=at 0.875 with label {$a$}] (0,0) rectangle (4,4);



 draw[lab dis=-0.3,

 -*-=0,->-=at 0.125 with label {$b$},

 -*-=0.25,->-=at 0.375 with label {$a$},

 -*-=0.5,-<-=at 0.625 with label {$b$},

 -*-=0.75,-<-=at 0.875 with label {$a$}] (2,-4) circle (2.5);

end{tikzpicture}

end{document}

You can place nodes on a path which should simplify the node positioning a lot. You might also want to factor out the arrow business into a style.

documentclass{article}

usepackage{tikz}

usetikzlibrary{decorations.markings}

begin{document}



begin{tikzpicture}[

  arrow inside/.style = {

    postaction={decorate},

    decoration={markings, mark=at position 0.5 with {arrow{stealth}}}

  }

  ]



  draw[arrow inside] (0,0) -- node [below] {$a$} (1,0);

  draw[arrow inside] (0,1) -- node [above] {$a$} (1,1);

  draw[arrow inside] (0,0) -- node [left] {$b$} (0,1);

  draw[arrow inside] (1,0) -- node [left] {$b$} (1,1);



end{tikzpicture}



end{document}

This can be an option

documentclass[tikz, border = 10pt]{standalone}



usepackage{pgfplots}

pgfplotsset{compat=newest}

usetikzlibrary{decorations.markings}



defnframes{30}

defframe{0}



begin{document}



foreach frame in {0,0,0,0,1,...,nframes}

{



pgfmathsetmacro{time}{frame / nframes}

pgfmathsetmacro{c}{20 + (3 - 20) / (1 + exp(-10 * (time - 0.6)))}

pgfmathsetmacro{a}{20 + (1 - 20) / (1 + exp(-8 * (time - 0.3)))}

pgfmathsetmacro{xrange}{3 + (180 - 3) / (1 + exp(-14 * (time - 0.6)))}

pgfmathsetmacro{yrange}{3 + (180 - 3) / (1 + exp(-10 * (time - 0.3)))}

pgfmathsetmacro{theta}{90 + (45 - 90) * time}

pgfmathsetmacro{phi}{0 + (25 - 0) * time}



pgfplotsset{

  border one/.style={

    thick,

    red,

    samples y  = 0,

    variable   = t,

    domain     = -xrange:xrange,

    postaction = {decorate},

    decoration = {markings,

                  mark = at position 0.48 with {arrow{stealth}},

                  mark = at position 0.52 with {arrow{stealth}}}

    },

  border two/.style={

    thick,

    green,

    samples y  = 0,

    variable   = t,

    domain     = -yrange:yrange,

    postaction = {decorate},

    decoration = {markings, mark = at position 0.5 with {arrow{stealth}}}

  }

}







begin{tikzpicture}

useasboundingbox (0, 0) rectangle (6, 6);

begin{axis} [

    hide axis,

    view               = {theta}{phi},

    domain             = -xrange:xrange,

    y domain           = -yrange:yrange,

    samples            = 20,

    samples y          = 20,

    unit vector ratio  = 1 1 1,

    declare function   = {

      u(x,y) = (c + a * cos(y)) * cos(x);

      v(x,y) = (c + a * cos(y)) * sin(x);

      w(x,y) = a * sin(y);

    }

  ]



  addplot3 [

    surf,

    color         = blue,

    opacity       = 0.01,

    faceted color = white,

    z buffer      = sort,

    fill opacity  = 0.5] ({u(x, y)}, {v(x, y)}, {w(x, y)});



  addplot3 [border one] ({u(t, yrange)}, {v(t, yrange)}, {w(t, yrange)});

  addplot3 [border one] ({u(t, -yrange)}, {v(t, -yrange)}, {w(t, -yrange)});

  addplot3 [border two] ({u(xrange, t)}, {v(xrange, t)}, {w(xrange, t)});

  addplot3 [border two] ({u(-xrange, t)}, {v(-xrange, t)}, {w(-xrange, t)});





end{axis}

end{tikzpicture}

}

end{document}

DISCLAIMER Just a fun animation, I'm aware it is not exactly what the OP asked for

A PSTricks solution just for fun purposes.

documentclass[pstricks,12pt]{standalone}

usepackage{pstricks-add}



begin{document}

pspicture[arrowinset=0,arrowscale=2](-4,-4)(4,4)

    curvepnodes[plotpoints=5]{0}{360}{3.5 t 45 add PtoC}{I}

    foreach i/l/a in {0/a/<,1/b/<,2/a/>,3/b/>}{%

        pcline[ArrowInside=-a](Ii)(Ithenumexpri+1)nbput{$l$}}

endpspicture

pspicture[arrowinset=0,arrowscale=2](-4,-4)(4,4)

    pnode(0,0){O}

    curvepnodes[plotpoints=5]{0}{360}{3.5 t 135 add PtoC}{I}

    foreach i/l in {0/a,1/b,2/a,3/b}{%

        qdisk([nodesep=3.5,angle=-45]{Ii}O){2pt}

        psarc{->}(0,0){3.5}{(Ii)}{(Ithenumexpri+1)}

        uput{8pt}[{(Ii)}](>Ii){$l$}}

endpspicture

end{document}

Note: ArrowInside is not available for psarc. I don't know why.

Another alternative approach using Metapost. Compile this one with lualatex.

documentclass[border=5mm]{standalone}

usepackage{luatex85}

usepackage{luamplib}

begin{document}

mplibtextextlabel{enable}

begin{mplibcode}

beginfig(1);

    path S, C;



    S = unitsquare shifted -(1/2, 1/2) scaled 100;

    C = fullcircle scaled 84 rotated 16 shifted 140 right;



    interim ahangle := 30;  % slimmer arrows...



    drawarrow subpath(0, 5/8) of S;

    drawarrow subpath(5/8, 13/8) of S;

    drawarrow subpath(4, 4-5/8) of S;

    drawarrow subpath(4-5/8, 4-13/8) of S;

    draw subpath(13/8, 4-13/8) of S;



    label.top("$a$", point 1/2 of S);

    label.top("$a$", point 5/2 of S);

    label.lft("$b$", point 3/2 of S);

    label.lft("$b$", point 7/2 of S);



    for t=0 upto 3:

        drawarrow subpath 2(t, t+1) of C;

        drawdot point 2t+3/4 of C withpen pencircle scaled 3;

        label(if odd t: "$b$" else: "$a$" fi, 9/8[center C, point 2t+7/4 of C]);

    endfor



endfig;

end{mplibcode}

end{document}