id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
5928	The backend should not silently discard initial consistent conditions or ignore initial inconsistent conditions	Francesco Casella	Karim Adbdelhak	"Please consider the following MWE, representing two point-mass objects which are rigidly connected to each other

{{{
model Consistent
  Real x1(start = 0, fixed = true);
  Real v1(start = 0, fixed = true);
  Real x2(start = 0, fixed = false);
  Real v2(start = 0, fixed = true);
  Real F;
equation
  der(x1) = v1;
  der(v1) = F;
  der(x2) = v2;
  der(v2) = -F+sin(time);
  x1 = x2;
end Consistent;
}}}

This model has two states after index reduction, and three {{{fixed = true}}} conditions, which are redundant but consistent. I would expect to get a warning about that, but I don't.

The following variant
{{{
model Inconsistent
  extends Consistent(v2(start = 1));
end Inconsistent;
}}}
has three redundant and ''inconsistent'' initial conditions, but is accepted and simulated, with the warning

{{{
[1] 11:41:30 Symbolic Warning
The model contains alias variables with conflicting start and/or 
nominal values. It is recommended to resolve the conflicts, because 
otherwise the system could be hard to solve. To print the conflicting
alias sets and the chosen candidates please use -d=aliasConflicts.
}}}

This warning would be appropriate in case there were no {{{fixed = true}}} modifiers and the tool had to pick between two potential states with different start value. But that is not the case here.

I guess this happens because index reduction here is handled by alias elimination. If that is the case, fixing this issue should be very easy
1. if the start value of an alias variable with {{{fixed = true}}} is the same as the selected representative variable, issue a warning that a redundant consistent initial equation has been eliminated
2. if the start value of an alias variable with {{{fixed = true}}} is ''not'' the same as the selected representative variable, issue an error that the model has inconsistent initial conditions:"	defect	closed	critical	1.16.0	Backend		fixed		Andrea Bartolini