module: trline_source_impedance
parameters: double zo, double zor
            double amp, double offset
inputs: double in double outr double outr_p
outputs: double out
classes:
static_variables: 
init: 
code:
if (zor <= 0.0 || zo < 0.0)
  {
   printf("error in 'trline_vsource': zor must be > 0.0 and zo >= 0.0\n");
   printf("  in this case, zor = %5.3e, zo = %5.3e\n",zor,zo);
   exit(1);  
  } 
out = zor/(zor+zo)*(amp/2.0*in+offset);
out += (zo-zor)/(zo+zor)*outr_p;
