Why the SS_threshold is 0.0

[jamestjsp]

According to documentation "Using a fixed order value, the maximum order and the threshold value are not taken into account." but is the select_order_SIM, SS_threshold is not passing and the algorithm_1 is always taking default value 0.0.

SIPPY/sippy/OLSims_methods.py

Line 171 in b699ab9

Ob, X_fd, M, n, residuals = algorithm_1(y, u, l, m, f, N, U_n, S_n, V_n, W1, O_i, 0.0,

[CPCLAB-UNIPI]

Dear jamestjsp,
when using a fixed order value, the function select_order_SIM is not evoked. Usually, when SS_fixed_order is not False, no information criteria is needed, therefore the threshold is set to 0.0. Otherwise, when specifying a threshold value (default value is 0.1) and maximum order, the values passed to algorithm_1 are the ones specified by the user.
Please, let us know if it is clear.

Best regards,

SIPPY team

[jamestjsp]

As you can see the select_order_SIM has no argument SS_threshold.

SIPPY/sippy/__init__.py

Line 735 in b699ab9

A, B, C, D, Vn, Q, R, S, K = OLSims_methods.select_order_SIM(y, u, SS_f, id_method, IC,

[RBdC]

Dear jamestjsp,
hoping you solved this old issue.
Anyway, here below I report the relative quotes of our guide for a better comprehension.

As you know, there are two main cases:

1. when an Information Criterion (IC) is NOT selected:
   After performing the singular value decomposition (SVD) scheduled for the SS identification,
   which allows building the suitable subspace from the original data space, the corresponding model order n (that is, the number of states) can be chosen by the settings:
   • I) a threshold value(SS_threshold, between 0.0 and 1.0) and the maximum order (SS_max_order, integer number);
   • II) a fixed order(SS_fixed_order, integer number).
   which are actually two alternatives methods.
   The threshold value implies that all singular values such that σi/σmax < SS_threshold are discarded, where σmax is the largest singular value, and σi is i-th singular value. The maximum order value (which acts in parallel) limits the order of the model to that value.
   Otherwise, using a fixed order value, the maximum order and the threshold value are not taken into account,
   and only a pure fixed order is considered
   By default: SS_threshold=0.1, while the other parameters are not specified.

2. When an IC is selected, the approach is totally different:
   the SS model order n is chosen in the defined range SS_orders, a list with two integer numbers; by default: SS_orders=[1,10] according to the IC selected.
   so that, SS_max_order and SS_threshold (and neither SS_fixed_order) are not to be passed to the corresponding functions.
   All the best
   SIPPY Team