% ex18.m4
.PS
cct_init
   "$v_i$" rjust; dot
   resistor(right_ dimen_) ; llabel(,R_i)
T: dot
   line right_ linewid/4
A: opamp with .In1 at Here

   line from A.In2 to (T,A.In2)
   resistor(down_ dimen_) ; rlabel(,R_g)
   ground(,T)

   line right_ dimen_ from A.Out
   diode(up_ dimen_); dot
   {line right_ linewid/2; dot; "$v_o$" ljust }
   resistor(left_ to (A.Out,Here)) ; rlabel(,R_o); dot
   { diode(down_ to A.Out); dot }
   line to (T,Here) then to T
.PE