Page 200 - Electrical Engineering Dictionary

mechanisms within control systems are fixed (2) a device for converting coded infor-
decision rule and optimization-based mech- mation to a form that can be understood by a
anism. Decision mechanisms can assume a person or machine.
hierarchical form — one may then talk about
a hierarchical decision structure. decoder source the coded signal input to
the decoder. In information theory the de-
decision support system a system whose coder source is modeled as a random process.
purpose is to seek to identity and solve prob-
lems. decoding (1) the act of retrieving the orig-
inal information from an encrypted (coded)
decision tree analysis decomposing a data transmission.
problem into alternatives represented by (2) the process of producing a single out-
branches where nodes (branch intersections) put signal from each input of a group of input
represent a decision point or chance event signals.
having probabilistic outcome. Analysis con- (3) the operation of the decoder. The in-
sists of calculating expected values associ- verse mapping from coded symbols to recon-
ated with the chain of events leading to the structed data samples. Decoding is the in-
various outcomes. verse of encoding, insofar as this is possible.

decision-directed adaptation a method decomposition (1) an operation per-
for adapting a digital equalizer in which de- formed on a complex system whose purpose
cisions at the output of the equalizer are used is to separate its constituent parts or subsys-
to guide the adaptive algorithm. See also tems in order to simplify the analysis or de-
adaptive algorithm, LMS. sign procedures.
1. For large-scale systems, decomposition
declaration phase or statement in which a is performed by neglecting links intercon-
new variable is requested; the declaration of necting subsystems. It is followed by design
a variable is based on the definition of its type of local control systems on the base of local
or class. This phase leads to a instantiation objectives and coordination, which enables
of the variable. reaching global goals. See also decentralized
control.
decode cycle the period of time during 2. For optimization algorithms, decompo-
which the processor examines an instruction sition is reached by resolving the objective
to determine how the instruction should be function or constraints into smaller parts, for
processed. This is the part of the fetch- example, by partitioning the matrix of con-
decode-execute cycle for all machine instruc- strains in linear programs followed by the so-
tion. lution of a number of low dimensional linear
programs and coordination by Lagrange mul-
decode history table a form of branch tipliers.
history table accessed after the instruction 3. For uncertainties, decomposition is per-
is decoded and when the branch address is formed to make their model trackable, for
available so that the table need only store a example, by dividing them into matched
Boolean bit for each branch instruction to in- and mismatched parts. See also matching
dicate whether this address should be used. conditions.
4. For linear time-invariant systems in
decoder (1) a logic circuit with N inputs state form, Kalman’s decomposition is a
and 2 N outputs, one and only one of which transformation of state matrix in a way that
is asserted to indicate the numerical value of indicates its controllable and observable,
the N input lines read as a binary number. controllable and unobservable, uncontrol-

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