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+//chapter12
+//example12.20
+//page256
+
+Vcc=8 // V
+Rb=360 // kilo ohm
+Rc=2 // kilo ohm
+gain_beta=100
+Vbe=0.7 // V
+
+// when Ic=0, Vce=Vcc i.e. Vce=8 and when Vce=0, Ic=Vcc/Rc i.e. Ic=8/2
+// so equation of load line becomes Ic=-0.5*Vce+4
+
+clf()
+x=linspace(0,8,5)
+y=-0.5*x+4
+plot2d(x,y,style=3,rect=[0,0,9,5])
+xtitle("dc load line","Vce(volts)","Ic(mA)")
+
+// since Vcc=Ib*Rb+Vbe we get
+Ib=(Vcc-Vbe)/Rb
+Ic=Ib*gain_beta
+Vce=Vcc-Ic*Rc
+
+printf("the operating point is %.3f V and %.3f mA \n",Vce,Ic)
+if Vce<Vcc/2+0.1 | Vce>Vcc/2-0.1 // check if V_CE is nearly half of V_CC
+    printf("circuit is mid-point biased \n")
+else 
+    printf("circuit is not mid-point biased. \n")
+end