A singular matrix error occurs when the circuit does not have a unique and finite solution. For example, a circuit containing a floating capacitor does not have a unique DC solution as the capacitor can be at any voltage. Also circuits with shorted inductors, voltage sources or a combination of both will fail with this error.
If you get this error, select menu . This will show any nodes with no DC path to ground - a common cause of singular matrix errors. If this doesn't show the cause, check your circuit generally.
If you think you circuit is OK then it is possible that the error is occurring because during the course of iterating to a solution, some node voltages or device currents reached very high values and the limited accuracy of the machine made it seem that the matrix was singular. This can happen with junction initialised iteration. If this is the case, try setting the option:
.OPTIONS NOOPITER
This will inhibit this mode and the simulator will start with source stepping. This method, and the others that follow, don't generally suffer from this problem.
Note that the simulation will abort if a singular matrix is detected in junction initialised iteration. It will not automatically attempt the other methods. This is because, by far the most common reason for singular matrices is circuit error.
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