The algorithm has reached convergence when the difference between the last iteration (k) and the current one ((\left. k + 1 \right))

[\begin{array}{ll} {\left| {v_{n}^{({k + 1})} - v_{n}^{(k)}} \right| \leq \mathtt{RELTOL} v_{n_{max}} + \mathtt{VNTOL},} & \ \end{array}]

where

[\begin{array}{ll} {v_{n_{max}} = \max\left( {\left| v_{n}^{({k + 1})} \right|,\left| v_{n}^{(k)} \right|} \right).} & \ \end{array}]

The RELTOL (RELative TOLerance) parameter, which default value is (10^{- 3}), specifies how small the solution update must be, relative to the node voltage, to consider the solution to have converged. The VNTOL (absolute convergence) parameter, which has (1\mu V) as default value, becomes important when node voltages have near zero values. The relative parameter alone, in such case, would need too strict tolerances, perhaps lower than computer round-off error, and thus convergence would never be achieved. VNTOL forces the algorithm to consider as converged any node whose solution update is lower than its value.