93Bxx Controllability, observability, and system structure

93B03  Attainable sets
93B05  Controllability
93B06  Relations between controllability and optimal solutions
93B07  Observability
93B10  Canonical structure
93B11  System structure simplification
93B12  Variable structure systems
93B15  Realizability of systems from input-output data
93B17  Transformation
93B18  Linearizability
93B20  Minimal systems representations
93B25  Algebraic methods
93B27  Geometric methods (including algebro-geometric)
93B28  Operator-theoretic methods, See also {47A57, 47N70}
93B29  Differential-geometric methods
93B30  System identification
93B35  Sensitivity (robustness)
93B36  ${H}^ \infty$-control
93B40  Computational methods
93B50  Synthesis problems
93B51  Design techniques (robust design, computer-aided design,
               etc.)
93B52  Feedback control
93B55  Pole and zero placement problems
93B60  Eigenvalue problems
93B99  None of the above but in this section