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The example *x*(*t*), *x*_{t}, *X*_{k}, *X*(*Z*), can be understood as follows.
A lower-case letter with a function argument (*t*)
denotes a continuous time function (rare).
Lower case with a subscript denotes a signal or filter
as a function of discrete time (common).
Upper case with subscript denotes a discrete Fourier transform.
*Z*-transforms are denoted by the function argument (*Z*).
Where a function argument is occasionally seen,
such as in ,it is generally a shorthand for .For a definition of the complex conjugate of filters,
see page .
`
`*aA* feedback filter (autoregression)
*bB* convolution filter
*cC* causal filter; reflected wave; cross-spectrum
*dD* downgoing wave
*E* escaping wave
*fF* component of layer matrix; force; generic function
*gG* component of layer matrix; analytic signal; causal garbage filter
*hH* admittance
*I* causal integration operator
*JKLMO* unused
*N* noise
*pP* phase shift; pressure; all-pass filter; generic input space
*qQ* quadrature filter; generic output space
*rR* impedance; reflection seismogram
*sS* *S* is spectrum; *s*_{t} is autocorrelation
*T* transmitted wave
*uU* upcoming wave; logarithm of *S*
*vV* velocity
*W* weighting function; vertical component of flow
*xX* generic input signal
*yY* generic output signal
phase

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Stanford Exploration Project

10/21/1998