# psinfo

Inquire about polytopic or parameter-dependent systems created with `psys`

## Syntax

```psinfo(ps)
[type,k,ns,ni,no] = psinfo(ps)
pv = psinfo(ps,'par')
sk = psinfo(ps,'sys',k)
sys = psinfo(ps,'eval',p)
```

## Description

`psinfo ` is a multi-usage function for queries about a polytopic or parameter-dependent system `ps` created with `psys`. It performs the following operations depending on the calling sequence:

• `psinfo(ps)` displays the type of system (affine or polytopic); the number `k` of `SYSTEM` matrices involved in its definition; and the numbers of `ns`, `ni`, `no` of states, inputs, and outputs of the system. This information can be optionally stored in MATLAB® variables by providing output arguments.

• `pv = psinfo(ps,'par')` returns the parameter vector description (for parameter-dependent systems only).

• `sk = psinfo(ps,'sys',k)` returns the k-th `SYSTEM` matrix involved in the definition of `ps`. The ranking k is relative to the list of systems `syslist` used in `psys`.

• `sys = psinfo(ps,'eval',p)` instantiates the system for a given vector p of parameter values or polytopic coordinates.

For affine parameter-dependent systems defined by the `SYSTEM` matrices S0, S1, . . ., Sn, the entries of `p` should be real parameter values p1, . . ., pn and the result is the LTI system of `SYSTEM` matrix

S(p) = S0 + p1S1 + . . .+ pnSn

For polytopic systems with `SYSTEM` matrix ranging in

Co{S1, . . ., Sn},

the entries of `p` should be polytopic coordinates p1, . . ., pn satisfying pj ≥ 0 and the result is the interpolated LTI system of `SYSTEM` matrix

$S=\frac{{p}_{1}{S}_{1}+\cdots +{p}_{n}{S}_{n}}{{p}_{1}+\cdots +{p}_{n}}$