I'm trying to do a DC analysis of following circuit. I want to sweep V_AB and voltage sources in the box. I tried to with following ngspice command, dc Vab -1.8 1.8 0.01 V1 0 1.8 0.1 Also I change the value of E1 as V1 (I was expecting to copy the value of V1 to E1). <-- I think here is the issue. Probaly, it should be syntax error, because I don't know correct way to do it with ngspice.