edge of the quantity is incorporated. See also
posterior statistics
.
prioritization coding
a coding scheme
whereby the position of the symbol in the
data steam indicates its weight.
priority encoder
an encoder with the ad-
ditional property that if several inputs are as-
serted simultaneously, the output number in-
dicates the numerically highest input that is
asserted.
prism
| air | metal (PAM) system
the
two-interface model of an ATR (attenuated
total reflection) system comprised of prism
|
air
| metal. Commonly known as PAM sys-
tem.
prismatic joint
a joint characterized by
a translation that is the relative displacement
between two successive links. This transla-
tion is sometimes called the joint offset.
private key cryptography
also known as
secret key cryptography. In such a crypto-
graphic system, the secret encryption key is
only known to the transmitter and the receiver
for whom the message is intended. The se-
cret key is used both for the encryption of the
plaintext and for the decryption of the cipher-
text. See also
public key cryptography
.
privileged instruction
an instruction that
can be executed only when the CPU is in priv-
ileged mode.
privileged mode
a mode of execution of
machine instructions in the CPU in which
certain special instructions can be executed
or data accessed that would otherwise be pro-
hibited. See also
user mode
.
PRMA
See
packet reservation multiple
access
.
probabilistic metric space
a generaliza-
tion of the notion of metric spaces onto the
uncertain systems by replacing a metric on a
given set
S by a distance distribution func-
tion
F , and a triangle inequality by a gen-
eralized inequality defined by triangle func-
tion
τ. A distance distribution functions be-
tween two elements
p, q ∈ S is defined as
a real function
F
pq
whose value
F
pq
(x) for
any real number
x is interpreted as the proba-
bility, the membership function, or the grade
of membership (depending on the type of the
uncertainty model) that the distance between
p and q is less than x. The simplest distance
distribution function is given by the unit step
(Heaviside) function 1 as follows:
F
pq
(x) = 1(x − d(p, q))
where
d is a standard metric. Then a proba-
bilistic metric space reduces to the standard
metric space. More precisely, a probabilis-
tic metric space (PMS) is defined as a triple
(S, F, τ) endowed with the following prop-
erties:
F
pq
(x) = 1(x) ⇐⇒ p = q
F
pq
= F
qp
F
pr
≥ τ F
pq
, F
qr
for all
p, q, r ∈ S. The types of the distri-
bution function and the triangle function are
related to the model of uncertainty and the
way of composition of the standard opera-
tions in the model.
probabilistic neural network
a term ap-
plied loosely to networks that exhibit some
form of probabilistic behavior but also ap-
plied specifically to a type of network devel-
oped for pattern classification based upon sta-
tistical techniques for the estimation of prob-
ability densities.
probability density function (PDF)
(1) a
function describing the relative probability of
outcomes of an experiment. For experiments
with discrete outcomes, the PDF is analogous
to a relative frequency histogram. For exper-
iments with continuous outcomes, the PDF
analogous to a relative frequency histogram
where the category bin widths are reduced to
c
2000 by CRC Press LLC