SpiceSharp.Algebra.SingularException : The matrix was found to be singular when eliminating row 3.

[marcin-golebiowski]

Could you please check why there is the exception: "SpiceSharp.Algebra.SingularException : The matrix was found to be singular when eliminating row 3." for circuit:

        [Test]
        public void When_SimplestCircuit_Expect_Reference()
        {
            var ckt = new Circuit(
                new VoltageSource("V1", "OUT", "0", 10),
                new BehavioralResistor("R1", "OUT", "0", "V(OUT,0)"));

            var op = new OP("Simple circuit"); 
            var refExport = new RealCurrentExport(op, "V1");
            op.ExportSimulationData += (sender, args) =>
            {
                Assert.AreEqual(-1, refExport.Value, 1e-8);
            };

            op.Run(ckt);
        }

The circuit works in LTSpice:

[svenboulanger]

I can already venture a guess here. In the first iteration, v(OUT) = 0, so this means that the resistor has i = V(OUT)^2 with 0 for all derivatives, which makes the matrix singular.

So the question is then, how can we fix this... Maybe I should make some minimum (GMIN) value for derivatives to make sure that a behavioral component always produces something...

[marcin-golebiowski]

Looks like that. Following test passed:

         [Test]
        public void When_SimplestCircuit_Expect_Reference()
        {
            var ckt = new Circuit(
                new VoltageSource("V1", "OUT", "0", 10),
                new BehavioralResistor("R1", "OUT", "0", $"V(OUT,0) + {1e-12}" ));

            var op = new OP("Simple circuit"); 
            var refExport = new RealCurrentExport(op, "V1");
            op.ExportSimulationData += (sender, args) =>
            {
                Assert.AreEqual(-1, refExport.Value, 1e-8);
            };

            op.Run(ckt);
        }

[svenboulanger]

Hey Marcin, does LTSpice generate some kind of warning messages (like adding a GMIN resistor to ground somehwere)?

EDIT: Reason I ask is because depending on the situation, this might be an issue for Spice# and not Spice#.Behavioral...

[marcin-golebiowski]

It's little funny but there was some error in the SPICE Error log:
"Questionable use of curly braces in "b§r1 out 0 r={v(out,0)}"
Error: undefined symbol in: "v"

However it was only about using of curly braces.
Following circuit:

Simple behavioral resistor circui
V1 OUT 0 10.0
R1 OUT 0 R=V(OUT,0)
.OP
.PROBE

doesn't generate any warnings.