Universal amplitude ratios for scaling corrections on Ising strips with fixed boundary conditions

We study the (analytic) finite-size corrections in the Ising model on the strip with fixed ($+-$) boundary conditions. We find that subdominant finite-size corrections to scaling should be to the form $a_k\mathrm{/}{N}^{2k-1}$ for the free energy $f_N$ and $b_k^{(n)}\mathrm{/}{N}^{2k-1}$ for inverse correlation length ${\xi }_n^{-1}$, with integer value of $k$. We investigate the set ${a_k, b_k^{(n)}}$ by exact evaluation and their changes upon varying anisotropy of coupling. We find that the amplitude ratios $b_k^{(n)}\mathrm{/}{a}_k$ remain constant upon varying coupling anisotropy. Such universal behavior are correctly reproduced by the conformal perturbative approach.