Mryntu

I have the nodes and arcs modeled in TikZ, but I'm scratching my head about how to draw the 'supply' and 'demand' double arrows (e.g. demand of 2 on node 1, supply of 2 on node 3). Can anybody help? Thanks

current code, which produces the nodes and arcs (ignoring dashed lines), the demand nodes, but not the double-tailed supply and demand arrows:

documentclass[]article

usepackagepgf, tikz
usetikzlibraryarrows, automata, positioning

begindocument
begintikzpicture
[roundnode/.style=circle,draw=black!50,thick,
supplynode/.style=circle,
 > = stealth, % arrow head style
 shorten > = 1pt, % don't touch arrow head to node
 auto,
 node distance = 3cm, % distance between nodes
 semithick % line style
]
 node at (0,0) [roundnode] (n1) 1;
 node at (2.5,2.5) [roundnode] (n2) 2;
 node at (0.0,5.0) [roundnode] (n3) 3;
 node at (5.0,0.0) [roundnode] (n4) 4;
 node at (5.0,4.0) [roundnode] (n5) 5;
 node at (10.0,5.0) [roundnode] (n6) 6;
 node at (10.0,0.0) [roundnode] (n7) 7;
 node at (7.5,2.5) [roundnode] (n8) 8;

 node at (-1.0, -1.0) [supplynode] (s1) 2;
 node at (2.5, 3.5) [supplynode] (s2) 1;
 node at (-1.0, 6.0) [supplynode] (s3) 2;
 node at (5.0,-1.0) [supplynode] (s4) 6;
 node at (6.0,4.0) [supplynode] (s5) 2;
 node at (11.0,0.0) [supplynode] (s7) 5;

 path[->] (n1) edge node 0 (n3);
 path[->] (n2) edge node 3 (n1);
 path[->] (n2) edge node 2 (n5);
 path[->] (n3) edge node 0 (n2);
 path[->] (n3) edge node 1 (n6);
 path[->] (n4) edge node 1 (n1);
 path[->] (n5) edge node 2 (n4);
 path[->] (n6) edge node 1 (n8);
 path[->] (n7) edge node 1 (n6);
 path[->] (n7) edge node 4 (n4);
 path[->] (n8) edge node 3 (n5);
 path[->] (n8) edge node 0 (n7);



endtikzpicture
enddocument

what the above code produces:

OK, I'm sure there's a better way to organize things inside the Tikz, but I have found a sufficient answer to my question myself. Posting here for posterity.

documentclass[]article

usepackagepgf, tikz
usetikzlibraryarrows, automata, positioning, arrows.meta

begindocument
begintikzpicture
[roundnode/.style=circle,draw=black!50,thick,
supplynode/.style=circle ,
 > = stealth, % arrow head style
 shorten > = 1pt, % don't touch arrow head to node
 auto,
 node distance = 3cm, % distance between nodes
 semithick % line style
]
 node at (0,0) [roundnode] (n1) 1;
 node at (2.5,2.5) [roundnode] (n2) 2;
 node at (0.0,5.0) [roundnode] (n3) 3;
 node at (5.0,0.0) [roundnode] (n4) 4;
 node at (5.0,4.0) [roundnode] (n5) 5;
 node at (10.0,5.0) [roundnode] (n6) 6;
 node at (10.0,0.0) [roundnode] (n7) 7;
 node at (7.5,2.5) [roundnode] (n8) 8;

 node at (-1.0, -1.0) [supplynode] (s1) 2;
 node at (2.5, 4.0) [supplynode] (s2) 1;
 node at (-1.0, 6.0) [supplynode] (d3) 2;
 node at (5.0,-1.5) [supplynode] (s4) 6;
 node at (6.5,4.0) [supplynode] (d5) 2;
 node at (11.5,0.0) [supplynode] (d7) 5;

 path[->] (n1) edge node 0 (n3);
 path[->] (n2) edge node 3 (n1);
 path[->] (n2) edge node 2 (n5);
 path[->] (n3) edge node 0 (n2);
 path[->] (n3) edge node 1 (n6);
 path[->] (n4) edge node 1 (n1);
 path[->] (n5) edge node 2 (n4);
 path[->] (n6) edge node 1 (n8);
 path[->] (n7) edge node 1 (n6);
 path[->] (n7) edge node 4 (n4);
 path[->] (n8) edge node 3 (n5);
 path[->] (n8) edge node 0 (n7);

 draw[-Implies,line width=1pt,double distance=2pt] (n1) -- (s1);
 draw[-Implies,line width=1pt,double distance=2pt] (n2) -- (s2);
 draw[-Implies,line width=1pt,double distance=2pt] (d3) -- (n3);
 draw[-Implies,line width=1pt,double distance=2pt] (n4) -- (s4);
 draw[-Implies,line width=1pt,double distance=2pt] (d5) -- (n5);
 draw[-Implies,line width=1pt,double distance=2pt] (d7) -- (n7);
endtikzpicture
enddocument

produces this, which is sufficient for my needs. Thanks @Zarko for the tip.

let me convert my comments to the answer ... with some off-topic sugestion :-) :

documentclass[tikz, margin=3mm]standalone
usetikzlibraryarrows.meta, automata,
 positioning,
 quotes

begindocument
 begintikzpicture[auto=left,
% node distance = 15mm and 15mm, % distance between nodes
 roundnode/.style = circle,draw=black!50,thick,
every edge/.style = draw, semithick, -Stealth, shorten > = 1pt,
 imp/.style = -Implies[], semithick, double distance=1pt
 ]
 beginscope[every node/.style=roundnode]
node at ( 0.0,0) (n1) 1;
node at ( 2.5,2.5) (n2) 2;
node at ( 0.0,5.0) (n3) 3;
node at ( 5.0,0.0) (n4) 4;
node at ( 5.0,4.0) (n5) 5;
node at (10.0,5.0) (n6) 6;
node at (10.0,0.0) (n7) 7;
node at ( 7.5,2.5) (n8) 8;
 endscope
 beginscope[every node/.style=circle]
node at (-1.0,-1.0) (s1) 2;
node at ( 2.5, 4.0) (s2) 1;
node at (-1.0, 6.0) (d3) 2;
node at ( 5.0,-1.5) (s4) 6;
node at ( 6.5, 4.0) (d5) 2;
node at (11.5, 0.0) (d7) 5;
 endscope
path (n1) edge ["0"] (n3)
 (n2) edge ["3"] (n1)
 (n2) edge ["2"] (n5)
 (n3) edge ["0"] (n2)
 (n3) edge ["1"] (n6)
 (n4) edge ["1"] (n1)
 (n5) edge ["2"] (n4)
 (n6) edge ["1"] (n8)
 (n7) edge ["1"] (n6)
 (n7) edge ["4"] (n4)
 (n8) edge ["3"] (n5)
 (n8) edge ["0"] (n7);
 beginscope[every edge/.style = draw,imp]
path (n1) edge (s1)
 (n2) edge (s2)
 (d3) edge (n3)
 (n4) edge (s4)
 (d5) edge (n5)
 (d7) edge (n7);
 endscope
endtikzpicture
enddocument

above mwe gives: