# Why can one assume in “infinite grid of resistors” that in the center there are diagonal nodes that have $-1$ and $+1$ currents?

Why can one assume in "infinite grid of resistors" that in the center there are diagonal nodes that have $-1$ and $+1$ currents?

As in the matrix $P$ in the following picture:

• Were you asked to find the equivalent resistance between those particular nodes? – The Photon Feb 3 '18 at 16:51
• @ThePhoton, further down the line, yes of course. – mavavilj Feb 4 '18 at 7:45