Finite-size scaling allows the extraction of a dimension from scaling
ds, as well as critical exponents for systems with a second-order phase transition. The calculation of
ds allows comparisons to be made with other expansions in dimension, in which
ds plays the role of the physical dimension. This is demonstrated by a numerical transfer-matrix study of the pure ferromagnetic Ising model in two and three dimensions, as well as for quenched random bonds in the two-dimensional Ising ferromagnet.
A transfer-matrix scaling technique is developed for randomly diluted systems and applied to the site-diluted Ising model on a square lattice. For each connected configuration between adjacent columns, the contribution of the respective transfer matrix to the decay of correlations is considered only as far as the ratio of the two largest eigenvalues, allowing an economical incorporation of configurational averages. Predictions for the phase boundary at and near the percolation and pure Ising limits, and for the correlation exponent \ensuremath{\eta} at those limits, agree with exactly known results to within 1% error with largest strip widths of only L=5. The exponent \ensuremath{\eta} remains near the pure value (1/4) for all intermediate concentrations until it turns over to the percolation value at the threshold.