PS
# ex05DPV.m4
darrow_init

Kalman: [
 fillval = 0.8

 boxht = 0.35
 boxwid = 1.5*boxht
 dx = boxht/5
 circlerad = boxht*3/8
 extlen=4*dx
 indel = boxht/3
 define(`dlthick',dlthick*3/4)

define(`overbar',`line right textht*0.8 \
 with .c at last box.c + ((`$1')*textht,0.7*textht)')

COb: box fill_ "CO"; overbar(0.5)
CO:box fill_ with .nw at last box.se+(dx,-dx) "CO"
CbOb: box fill_ with .nw at last box.se+(dx,-dx) "CO"
 overbar(-0.5); overbar(0.5)
CbO: box fill_ with .nw at last box.se+(dx,-dx) "CO"; overbar(-0.5)

 dline(from CbO.s down_ dx,,t,,!-)
 dright
{Sum: circle invis at (CO,Here)}
 darrow(to Sum.e)

SW: (COb.w,Sum.s)+(-3*dx-extlen/2,-dx)
NE: (CbO.e,COb.n)+(dx,dx)
 right_;
SB: shadebox(box wid NE.x-SW.x ht NE.y-SW.y with .sw at SW)

U: COb.w-(3*dx+extlen,0)
 {"svg_it(U)" wid 0.1 rjust at U}
 dline(from U right_ extlen+dx,,t,,|-)
TU: dtee(R)
 {darrow(to COb.w,t)}
 dline(to (Here,CO),t,t)
{Dum: circle invis at (Here,Sum)}
 dtee(L)
 {darrow(to CO.w,t)}
{D: box "D" wid boxwid/2 ht boxwid/2 at 0.5<Here,Dum.n>}
 darrow(to D.n,t)
 darrow(from D.s to Dum.n,,,,,,!-)

 dline(up_ from CO.n to (CO,COb)-(0,indel),,t,,!-)
 dleft; darrow(to (COb.e,Here))

 dline(up_ from CbOb.n to (CbOb,COb),,t,,!-)
 dleft; darrow(to COb.e)

 dline(from CbO.n-(indel,0) up_ CbOb.y-CbO.n.y,,t,,!-)
 dleft; darrow(to CbOb.e)

 dline(up_ from CbO.n to (CbO,CO),,t,,!-)
 dleft
 dline(to (CbOb.w,Here)); darrow(to CO.e)

 dline(up_ from CbO.n+(indel,0) to (CbO,COb)+(indel,indel),,t,,!-)
 dleft; darrow(to (COb.e,Here))

 darrow(from CO.s to Sum.n,,,,,,!-)

 darrow(left_ from Sum.w to Dum.e)
 dline(from Dum.w to (SB.w-(0.1,0),Dum)); darrow(to (U,Here))
   {"svg_it(Y)" rjust}
 move left 0.23

 circle at Sum
 circle at Dum
 ]
Coxeter: [
# Coxeter.m4

 customlinethick = 1.5

 linethick = customlinethick
 define(`dotrad_',`(3/2*linethick pt__)')

 Orig: (0,0)
 for i=0 to 4 do { P[i]: dot(at (i*linewid,0)) }
 line from Orig to P[4]
 P[-1]: dot(at (Rect_(linewid, 120))); line to Orig
 P[-2]: dot(at (Rect_(linewid,-120))); line to Orig

Pa: dot(at P[4]+(linewid,0));         "svg_it(a)" at last [].n above
 arrow from P[4] to Pa chop linewid/4
Pd: dot(at Pa+(linewid,0));           "svg_it(d)" at last [].w rjust
Pe: dot(at Pd+(linewid,0));           "svg_it(e)" at last [].n above
Pf: dot(at Pe+(linewid,0));           "svg_it(f)" at last [].n above
Pb: dot(at Pd+(Rect_(linewid,120)));  "svg_it(b)" at last [].w rjust
Pc: dot(at Pd+(Rect_(linewid,-120))); "svg_it(c)" at last [].w rjust
 line from Pb to Pd then to Pc
 line from Pd to Pf

 define(`customarc',
  `pushdef(`dfillcolor',`0.7,0.7,0.7') linethick_(0.4); dnl
   Darc(,centre=`$1';rad=linewid;startdeg= (`$2');enddeg=(`$3');
     thick=linewid/6; wid=linewid*0.3; ht=linewid/6; ends=<->)
   linethick_(customlinethick); popdef(`dfillcolor')')

 customarc((linewid,-linewid/3), 25,155)
  "svg_it(d)" at (linewid,linewid*2/3)
 customarc((2*linewid,-linewid/3), 25,155)
  "svg_it(e)" at (2*linewid,linewid*2/3)
 customarc((3*linewid,-linewid/3), 25,155)
  "svg_it(f)" at (3*linewid,linewid*2/3)
 customarc(Orig,130,230);                  "svg_it(a)" at (Rect_(linewid,180))
 customarc(Orig, 10,110);                  "svg_it(b)" at (Rect_(linewid, 60))
 customarc(Orig,-110,-10);                 "svg_it(c)" at (Rect_(linewid,-60))

 ] with .sw at Kalman.se+(15bp__,0)
[
 linethick = 5
 Darrow(right_ Coxeter.wid,
   thick=0.3;wid=0.55;ht=0.55;ends=<->; innershade=(0,1,1);outline=(0,0,1))
 ] with .sw at Coxeter.nw+(0,0.3)
PE