id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
4712	Errors in the selection of start attributes within alias variable sets	Francesco Casella	Patrick Täuber	"Please run the {{{PowerGrids.Electrical.Test.OneBusTransmissionLineOneLoad}}} test case from the attached library. I get the following warning:
{{{
Translation Warning
Alias set with conflicting start values
 * Candidate: transmissionLine.portB.i.re(start = -577.3502691896258, confidence number = 9)
 * Candidate: loadPQ.port.i.re(start = -577.3502691896258, confidence number = 9)
 * Candidate: transmissionLine.portA.i.re(start = 577.3502691896258, confidence number = 9)
=> Select value from transmissionLine.portA.i.re(start = 577.3502691896258) for variable: transmissionLine.iB.re
}}}
There are two fishy things in here. First of all, the start attribute of {{{loadPQ.port.i.re}}}, which is {{{loadPQ.port.iStart.re}}}, should be +577.35, not -577.35. In fact, the value of that parameter is correctly reported in the variable broser as being +577.35, but for some reason it gets the wrong sign in the alias set start attribute selection. The other two reported start attributes are correct.

Secondly, I'm not sure why the start attribute of {{{transmissionLine.portA.i.re}}} is selected to initialize the alias variable {{{transmissionLine.iB.re}}}, which is among the tearing variables of the system. That could be ok, but then, as the two values sum to zero in the alias set, the initial guess value for transmissionLine.iB.re should be -577.35; unfortunately, turning on LOG_NLS_V reveals that the initial guess value is actually +577.35, and that somehow leads to a solver failure.

Both issues should be fixed for consistency and correctness. I tried to reproduce the problem on a simpler test case, but I failed, so please check this larger case out. As the model is confidential, it was encrypted with the PGP key stored on dev.openmodelica.org, as agreed."	defect	closed	critical	1.13.0	Backend		invalid		Martin Sjölund