Informatics Report Series
http://hdl.handle.net/1842/3390
2018-02-25T15:29:58ZComputational mechanisms for action selection
http://hdl.handle.net/1842/20257
Computational mechanisms for action selection
Tyrrell, Toby
Imagine a zebra in the African savannah. At each moment in time this zebra has to
weigh up alternative courses of action before deciding which will be most beneficial
to it. For instance, it may want to graze because it is short of food, or it may want
to head towards a water hole because it is short of water, or it may want to remain
motionless in order to avoid detection by the predator it can see lurking nearby. This is
an example of the problem of action selection: how to choose, at each moment in time,
the most appropriate out of a repertoire of possible actions.
This thesis investigates action selection in a novel way and makes three main contribu¬
tions. Firstly, a description is given of a simulated environment which is an extensive
and detailed simulation of the problem of action selection for animals. Secondly, this
simulated environment is used to investigate the adequacy of several theories of ac¬
tion selection such as the drive model, Lorenz's hydraulic model and Maes' spreading
activation network. Thirdly, a new approach to action selection is developed which
determines the most appropriate action in a principled way, and which does not suffer
from the inherent shortcomings found in other methods.
1993-01-01T00:00:00ZRobot dynamics algorithms
http://hdl.handle.net/1842/18179
Robot dynamics algorithms
Featherstone, Roy
In this dissertation I introduce a new notation for representing
rigid-body dynamics, and use it to describe a number of methods for
calculating robot dynamics efficiently.
The notation (called spatial notation) is based on the use of 6-
dimensional vectors (called spatial vectors) which combine the linear
and angular aspects of rigid-body dynamics. Spatial vectors are
similar to quantities called screws and motors. The use of spatial
notation allows a more concise treatment of problems in rigid-body
dynamics than is possible by the conventional vector approach by
reducing the number of quantities required to describe a system and
the number and size of equations relating those quantities. I consider both forward and inverse robot dynamics, though I am
concerned mainly with forward dynamics. Three basic algorithms are
described: the recursive Newton-Euler method for inverse dynamics,
and the composite-rigid-body and articulated-body methods for forward
dynamics. The articulated-body method is new, and is based on the
use of quantities called articulated-body inertias which relate the
force applied to a member of a linkage to the acceleration induced in
that member, taking into account the effect of the rest of the link¬
age. Once the basic algorithms have been introduced, I consider some
aspects of their implementation on a computer, then I describe vari¬
ous extensions of the basic algorithms to cater for generalisations
of the robot's structure, including multiple-degree-of-freedom joints
and branched kinematic chains. Finally, I consider the problem of
simulating contact and impact between the robot and its environment.
1984-01-01T00:00:00ZThe Polyadic pi-Calculus: A Tutorial
http://hdl.handle.net/1842/6050
The Polyadic pi-Calculus: A Tutorial
Milner, Robin
The pi-calculus is a model of concurrent computation based upon the notion of naming. It is first presented in its simplest and original form, with the help of several illustrative applications. Then it is generalized from monadic to polyadic form. Semantics is done in terms of both a reduction system and a version of labelled transitions called commitment; the known algebraic axiomatization of strong bisimilarity is given in the new setting, and so also is a characterization in modal logic. Some theorems about the replication operator are proved.
Justification for the polyadic form is provided by the concept of sort, sorting and sort discipline which it supports. Several illustrations of different sortings are given. One example is the presentation of data structures as processes which respect a particular sorting; another is the sorting for a known translation of the lambda-calculus in to pi-calculus. For this translation, the equational validity of beta-conversion is proved with the help of replication theorems. The paper ends with an extension of the pi-calculus to w-order processes, and a brief account of the demonstration by Davide Sangiorgi that higher-order processes may be faithfully encoded at first-order. This extends and strengthens the original result of this kind given by Bent Thomsen for second-order processes.
This report was published in F. L. Hamer, W. Brauer and H. Schwichtenberg, editors, Logic and Algebra of Specification. Springer-Verlag, 1993.
1991-01-01T00:00:00ZValue Function Approximation on Non-Linear Manifolds for Robot Motor Control
http://hdl.handle.net/1842/3714
Value Function Approximation on Non-Linear Manifolds for Robot Motor Control
Sugiyama, Masashi; Hachiya, Hirotaka; Towell, Christopher; Vijayakumar, Sethu
The least squares approach works efficiently in
value function approximation, given appropriate basis functions.
Because of its smoothness, the Gaussian kernel is a
popular and useful choice as a basis function. However, it
does not allow for discontinuity which typically arises in realworld
reinforcement learning tasks. In this paper, we propose
a new basis function based on geodesic Gaussian kernels,
which exploits the non-linear manifold structure induced by
the Markov decision processes. The usefulness of the proposed
method is successfully demonstrated in a simulated robot arm
control and Khepera robot navigation.
2007-04-01T00:00:00Z