Why does node analysis have a ground node?
The node analysis works with the potential of the nodes, and the potential is always relative to some point where we take it zero. Zero, like the potential of the ground. The "ground" means only U=0 for the chosen point. It need not be a physically real grounding.
Why the reference?
You need to find the potential of the nodes. The potential is defined with respect to something- with respect to a reference point.
Show your problem and your attempt to solve it with nodal analysis.
Okay, thanks! Read a little more about it. I'm clear now. It wasn't related to a problem. Just a general doubt.
Well, you can assign the notations U1, U2, U3, U4... to the nodes and write up all the equations, but you always get one less independent equations than the number of nodes. As an example, you have 4 nodes, and at the end you arrive to the solution U2=U1+6, U3=U1-2, U4=U1+10. You can choose any value for U1, but U1=0 is the simplest. If you fancy, it can be U1=1.4141 :)
It is not necessary to have a ground Node in Node Analysis. I never do any grounding in Node analysis.
As ehild said you can take U1 zero or 1.414 or just leave it to U1.
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