- x (bold, non-italic typeface) Matrix or vector
- x (non-bold, italic typeface) Scalar or array
- nf Number of frequency lines
- nc Number of control channels
- no Number of output signals
- ns Number of samples in a signal
- nos Number of samples in an oversampled output signal
- Gvv CPSD matrix for the output signals
- Gxx CPSD matrix for the responses (i.e. the specification)
- Hxv Transfer function matrix between the responses and the output signals
- X Response spectra (FFT)
- V Output spectra (FFT)
- T Transformation matrix
- A State or system matrix for state space equations of motion
- B Input matrix for state space equations of motion
- C Output matrix for state space equations of motion
- D Feedthrough or feedforward matrix for state space equations of motion
- x State vector for state space equations of motion
- y Output vector for state space equations of motion
- u Input vector for state space equations of motion
- M Mass matrix for 2nd-order differential equations of motion
- C Damping matrix for 2nd-order differential equations of motion
- K Stiffness matrix for 2nd-order differential equations of motion
- ⬚+ Pseudoinverse of a matrix
- ⬚H Complex-conjugate transpose of a matrix (hermitian)