id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
4329	Add warning about conflicting start values	Francesco Casella	Patrick Täuber	"Consider the following test case:
{{{
loadString(""
type T = Real(start = 10);
model Test
  T x;
  Real y(start = -10);
  Real z(start = -4);
  Real w;
equation
  x = y;
  x + z = 0;
  (x-3)*(x+11) = 0;
  (w-10)*(w+4) = 0;
end Test;
"");getErrorString();
setCommandLineOptions(""-d=initialization"");getErrorString();
simulate(Test, simflags=""-lv=LOG_NLS"");getErrorString();
}}}

The last equation requires an iterative solution with unknown {{{w}}}, and OMC appropriately issues the following warning:
{{{
Warning: Iteration variables with default zero start attribute in nonlinear equation system:
         w:VARIABLE()  type: Real
}}}

However, there is another issue with the first three equations that should also be reported. There are three alias variables, {{{x, y, z}}}. {{{x}}} has a start value defined with a lower priority, while {{{y}}} and {{{z}}} have a higher priority start value, according to Section 8.6.2 of the Modelica Specification. As the priority is the same, either could be chosen, leading to a different solution of the system.

As this is potentially dangerous for the convergence of the solution, I would suggest that a warning is issued in all the cases where such a variable is the unknown or tearing variable of an implicit system to be solved iteratively, pointing out: 
- the conflicting values with the same priority
- the value that was selected by OMC as initial guess for the solver"	defect	closed	high	1.13.0	Backend		fixed