% sfg.m4
.PS
sfg_init( 1.2 )   # scale default size by 1.2
ifelse(ifmpost(T)`'ifpostscript(T),,`command "{\small"')

# Graph 1
T:[
 Ft: sfgnode(,f(t),sfgbelow)
     sfgline(,1/K)
 Y1: sfgnode(,y_1,sfgbelow rjust)
     sfgline(,K/M)
 DDY2: sfgnode(,\ddot{y}_2,sfgbelow rjust)
     sfgline(,s^{-1})
 DY2: sfgnode(,`\dot{y}_2=x_2',sfgbelow ljust)
     sfgline(,s^{-1})
 Y2: sfgnode(,y_2=x_1,sfgbelow ljust)
 
 sf = 1
   sfgarc(from DY2 to DDY2,-B/M,below,,sf)
   sfgarc(from Y2 to DDY2,-K/M,above,ccw,sf)
   sfgarc(from Y2 to Y1,1,sfgabove,,sf)
 ]

# Graph 2
B: [
 R1: sfgnode(,r_1,sfgabove)
     sfgline(,1)
 X1: sfgnode(,\;x_1,ljust)
 R2: sfgnode(at R1+(0,-1),r_2,sfgabove)
     sfgline(,1)
 X2: sfgnode(,\;x_2,ljust)
     sfgarc(from X1 to X2,a_{21}\;,rjust,ccw)
     sfgarc(from X2 to X1,\;a_{12},ljust,ccw)
 
     sfgself(at X1,,q_{11})
     sfgself(at X1,R,\;a_{11},ljust,cw,1.5)
     sfgself(at X2,-90,a_{22},sfgbelow)
 ] with .nw at T.sw + (0,linewid/2)

# Graph 3
G3: [ sfg_init( 0.85,0.35/2 )   # change node spacing and increase node size
 for_(1,4,1,`N`'m4x: sfgnode(,m4x,,fill_(0.9))
   sfgself(at N`'m4x,-90,P_{m4x},,cw)
   ifelse(m4x,4,,`sfgline(,G_{m4x},sfgbelow)') ')
 sfgarc(from N2 to N1,F_2,sfgabove,ccw,)
 sfgarc(from N3 to N1,F_3,sfgbelow,ccw,1.4)
] with .sw at B.se + (linewid/2,0)

# Tucked between two big graphs
A: [ sfg_init( 0.75,0.15 )
   arrow right linewid*2/3
 P: sfgnode(,p)
   sfgself(,90,a,below,cw)
   arrow from P.e "b" below
 Q: sfgnode(,q)
#R: sfgnode(at Q+(Q-P),r) # for dpic
 R: sfgnode(at Q+(Q.x-P.x,Q.y-P.y),r) # for gpic
   sfgarc(from Q to R,c,above,cw)
   sfgarc(from R to Q,d,below,cw)
   sfgself(at R,-90,e,above,cw)
   arrow right linewid*2/3 from R.e
 ] with .sw at G3.nw+(0,0.0)

ifelse(ifmpost(T)`'ifpostscript(T),,`command "}%"')
.PE