Hi

I have a general question about the warning "Zero diagonal found in Jacobian"

I use spectre(7.2) to simulate some designs and I get sometimes this warning "Zero diagonal found in Jacobian" (as in the example below), even if the simulation converges and the results *seems* correct.

what's the effect of a " Zero diagonal found in Jacobian" on the simulation results ?

Is it possible that Jacobian reordering lead to convergence problem or error/innacuracy in the results ?

Thanks for your help,

Best Regards !

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Stability Analysis `stb': freq = (1 mHz -> 20 GHz)

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Zero diagonal found in Jacobian at `I4.M0:int_s' and `I4.M0:int_s'.

Reordering Jacobian.

Zero diagonal found in Jacobian at `I4.I89.M13:int_s' and `I4.I89.M13:int_s'.

Reordering Jacobian.

Trying `homotopy = gmin'.

Maximum value achieved for any signal of each quantity:

V: V(net176) = 3.3 V

I: I(V13:p) = 4.268 mA

stb: freq = 2.154 mHz (2.51 %), step = 159.2 uHz (251 m%)

stb: freq = 10 mHz (7.52 %), step = 738.8 uHz (251 m%)

stb: freq = 46.42 mHz (12.5 %), step = 3.429 mHz (251 m%)

stb: freq = 215.4 mHz (17.5 %), step = 15.92 mHz (251 m%)

stb: freq = 1 Hz (22.6 %), step = 73.88 mHz (251 m%)

stb: freq = 4.642 Hz (27.6 %), step = 342.9 mHz (251 m%)

stb: freq = 21.54 Hz (32.6 %), step = 1.592 Hz (251 m%)

stb: freq = 100 Hz (37.6 %), step = 7.388 Hz (251 m%)

stb: freq = 464.2 Hz (42.6 %), step = 34.29 Hz (251 m%)

stb: freq = 2.154 kHz (47.6 %), step = 159.2 Hz (251 m%)

stb: freq = 10 kHz (52.6 %), step = 738.8 Hz (251 m%)

stb: freq = 46.42 kHz (57.6 %), step = 3.429 kHz (251 m%)

stb: freq = 215.4 kHz (62.7 %), step = 15.92 kHz (251 m%)

stb: freq = 1 MHz (67.7 %), step = 73.88 kHz (251 m%)

stb: freq = 4.642 MHz (72.7 %), step = 342.9 kHz (251 m%)

stb: freq = 21.54 MHz (77.7 %), step = 1.592 MHz (251 m%)

stb: freq = 100 MHz (82.7 %), step = 7.388 MHz (251 m%)

stb: freq = 464.2 MHz (87.7 %), step = 34.29 MHz (251 m%)

stb: freq = 2.154 GHz (92.7 %), step = 159.2 MHz (251 m%)

stb: freq = 10 GHz (97.7 %), step = 738.8 MHz (251 m%)

Gain margin = 40.6864 dB at frequency = 642.509 MHz.

Phase margin = 86.7804 Deg at frequency = 12.8495 MHz.