Specify case with one coefficient and one variable in Modelica.Electrical.Spice3.Additionals.poly

[beutlich]

Only for one coefficient and one variable the polynomial is evaluated as linear function (with vanishing absolute term).

Closes #2794.

[HansOlsson]

Looks correct, but since it is so weird it would be helpful with additional documentation:
E.g. https://www.macspice.com/ug/secC.html explains the special case as:

Note: if the polynomial is one-dimensional and exactly one coefficient is specified, then SPICE assumes it to be p1 (and p0 = 0.0), in order to facilitate the input of linear controlled sources.

[beutlich]

Looks correct, but since it is so weird it would be helpful with additional documentation:
E.g. https://www.macspice.com/ug/secC.html explains the special case as:

Note: if the polynomial is one-dimensional and exactly one coefficient is specified, then SPICE assumes it to be p1 (and p0 = 0.0), in order to facilitate the input of linear controlled sources.

Yes, agreed. I just was not sure which Spice source we should cite here.