## 7 Options common to all frontends

All frontends for optimization and for result statistics (nonlin_min, nonlin_residmin, nonlin_curvefit, residmin_stat, curvefit_stat)accept the following options, settable with optimset.

These options are handled within the frontend.

`diffp`
  Column vector of fractional intervals (doubled for central intervals) supposed to be used by gradient or Jacobian functions performing finite differencing. Default: `.001 * ones (size (parameters))`. The default function for finite differencing will use these as absolute intervals for parameters with value zero.
`diff_onesided`
  Logical column vector indicating the parameters for which one-sided intervals should be used by gradient or Jacobian functions performing finite differencing. Default: `false (size (parameters))`.
`cstep`
  Scalar step size for complex step derivative approximation of gradients or Jacobians. Default: 1e-20.
`parallel_local`
  Logical scalar, default: `false`. If the `parallel` package, `version >= 2.0.5`, is loaded, estimate gradients of objective function and Jacobians of model function and of constraints in parallel processes. Works for default (real) finite differences and for complex step derivatives. Due to overhead, a speed advantage can only be expected if objective function, model function or constraint functions are time consuming enough. Additionally, this setting is also passed to the individual optimization backends, which may also consider this option (see documentation of backends). If this option is set to `true`, a warning (ID: `optim:parallel_local`) will be issued if no `parallel` package of a correct version is loaded.
`fixed`
  Logical column vector indicating which parameters are not optimized, but kept to their inital value.