The initial nonlinear feasibility tolerance (INFTOL) and the final nonlinear feasibility tolerance (FNFTOL) are both used by the nonlinear solver in the same manner that the initial linear and final linear feasibility tolerances are used by the linear solver. For information on how and why these tolerances are useful, refer to the section ILFTOL and FLFTOL . Default values for these tolerances are, respectively, 0.001 and 0.000001.