optim_doc: siman

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### 1.4 Simulated annealing backend siman of scalar optimization

A simulated annealing (stochastic) optimizer, changing all parameters at once in a single step, so being suitable for non-bound constraints.

No gradient or hessian of the objective function is used. The settings `MaxIter`, `fract_prec`, `TolFun`, `TolX`, and `max_fract_change` are not honoured.

Accepts the additional settings `T_init` (initial temperature, default 0.01), `T_min` (final temperature, default 1.0e-5), `mu_T` (factor of temperature decrease, default 1.005), `iters_fixed_T` (iterations within one temperature step, default 10), `max_rand_step` (column vector or structure-based configuration of maximum random steps for each parameter, default 0.005 * pin), `stoch_regain_constr` (if `true`, regain constraints after a random step, otherwise take new random value until constraints are met, default `false`), `trace_steps` (set field `trace` of outp with a matrix with a row for each step, first column iteration number, second column repeat number within iteration, third column value of objective function, rest columns parameter values, default `false`), and `siman_log` (set field `log` of outp with a matrix with a row for each iteration, first column temperature, second column value of objective function, rest columns numbers of tries with decrease, no decrease but accepted, and no decrease and rejected.

Steps with increase `diff` of objective function are accepted if `rand (1) < exp (- diff / T)`, where `T` is the temperature of the current iteration.

If regaining of constraints failed, optimization will be aborted and returned value of cvg will be `0`. Otherwise, cvg will be `1`. Returned structure outp, additionally to the possible fields `trace` and `log` described above, will have the fields `niter` and `user_interaction`.

Interpretation of `Display`: if set to `"iter"`, an informational line is printed after each iteration.

If `parallel_local` is equivalent to `true`, the objective function is evaluated for several parameter combinations in parallel. If `parallel_local` is set to an integer `> 1`, this is the maximal number of parallel processes; if it is `<= 1`, the maximal number will be the number of available processor cores. The course of optimization won’t be changed by parallelization, provided the random number generator starts with the same state. To achieve this, some of the parallel results are discarded, causing the speedup to be smaller if the rate of acceptance of results is high. Also, due to overhead, there won’t be any speedup, but even a slowdown, if the objective function is not computationally extensive enough.

Honours options `save_state` and `recover_state`, described for the frontend.

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