Hi everyone,
Currently I am attempting to run a dc sweep simulation by sweeping the power supply from one voltage to another voltage using Cadence IC5. I used the default setting in ADE (Analog Design Envinronment) and start to simulate using spectre.

Eventually, the spectre simulator found zero diagonal at certain nets and trying to reorder Jacobian. Anyone know what is this reordering Jacobian means and how to solve this problem since spectre simulator took more than half hour to simulate. Any setting to change in order to speed up or avoid zero diagonal? Is it due to the design, simulator, models? In certain cases, the simulator do not manage to get a solution. Hope to get explaination and ways to overcome this problem. By the way, how to ensure simulator manage to get the convergence using homotopy gmin/source which always give faster result compare to other convergence method. Thanks.

******************
DC Analysis `dcOp'
******************
Important parameter values:
   reltol = 1e-03
   abstol(I) = 1 pA
   abstol(V) = 1 uV
   temp = 35 C
   tnom = 27 C
   tempeffects = all
   gmin = 1 pS
   maxrsd = 0 Ohm
   mos_method = s
   mos_vres = 50 mV
Trying `homotopy = gmin'.
Continuation method failed.  Step size too small.
Trying `homotopy = source'.
Trying `homotopy = dptran'.
Zero diagonal found in Jacobian at `net172' and `net172'.
Reordering Jacobian.

In particular, did you look at or near net172 to find out what the problem was? As Sven says, in particular look for nodes that are floating or a loop of shorts.

The problem looks as if it occurred on the first sweep point, which is another clue.

-Ken