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%3Stanford University Computer Science Reports
%3List Number 9↔? 1980%1

@Listed here are abstracts of the most recent reports published by the
Department of Computer Science at Stanford University.

@%3Request Reports:%1 Complete the enclosed order
form, and return the entire order form page (including mailing label) 
as soon as possible.  In many cases we can print only a limited number of copies,
and requests will be filled on a first come, first served basis as the reports
become available.  If the code
(FREE) is printed on your mailing label, you will not be charged for hardcopy.
This exemption from payment is limited primarily to libraries.  (The costs
shown include all applicable sales taxes.  %2Please send
no money now, wait until you get an invoice%1.)

@%3Alternatively:%1 Copies of most Stanford CS Reports may be obtained by writing
(about 2 months after the "%2Most Recent CS Reports%1" listing) to 
%2National
Technical Information Service%1, 5285 Port Royal Road, Springfield, Virginia 22161.
Stanford Ph.D. theses are available from %2University Microfilms%1, 300 North
Zeeb Road, Ann Arbor, Michigan 48106.
.skip

%3STAN-CS-80-806:%1
.once preface 0
@%2On the Approximate Solution of Hyperbolic Initial-Boundary Value Problems%1
by William M. Coughran, Jr. (Thesis, 177 pages, June 1980)

@Hyperbolic initial-boundry value problems arise in a number of scientific
disciplines, such as meteorology, ocanography, geophysics, aerodynamics, acoustics,
and magnetohydrodynamics.  These problems usually cannot be solved analytically,
so approximate methods must be used.  Unfortunately, the construction of stable
finite difference approximations is a subtle matter, which often confuses the
practitioner; the existing theories for establishing the well-posedness of
continuous initial-boundary value problems and the stability of discrete analogs
involve the verification of complicated algebraic conditions.  Moreover, the
stability theory fo discrete initial-boundary value problems in more than one
space dimension is not well developed.

@In this thesis, the existing stability theory for discrete initial-boundary value
problems, which has only been applied to (essentially) salar model problems, is
used to analyze the stability of some %22 %4x %22%1 model problems, not written
in characteristic variables; it is noted that the most accurate interior/boundary
difference scheme combinations are the least stable to perturbations in the
coefficients.  (A practical numerical procedure for verifying the stability of
discrete initial-boundary value problems is also introduced.)  The stability
results for %22 %4x %22%1 systems can be used in the stability analysis of larger
systems where characteristics occur only singly and in pairs; in particular,
discretizations of the wave equation, the shallow  water equations, and the Eulerian
equations for gas dynamics, which involve boundary conditions written in "natural"
variables, are examined.  The stability theory is also extended to multi-dimensional
initial-bondary value problems by means of the concept of "tangential dissipativity";
as an application, a tangentially dissipative leap-frog metho is shown to be stable
with Euler boundary conditions for a two-dimensional wave equation problem.  The
viability and limitations of the theory are demonstrated with some computational
experiments.  Finally, combining stability results with accuracy considerations,
various approximations and boundary conditions are ranked.
.skip

%3STAN-CS-80-807:%1
.once preface 0
@%2Path-Regular Graphs%1 by David W. Matula and Danny Dolev
(39 pages, June 1980)

@A graph is vertex-[edge-]path-regular if a list of shortest paths, allowing
multiple copies of paths, exists where every pair of vertices are the endvertices
of the same number of paths and each vertex [edge] occurs in the same number of
paths of the list.  The dependencies and independencies between the various
path-regularity, regularity of degree, and symmetry properties are investigated.
We show that every connected vertex-[edge-]symmetric graph is vertex-[edge-]path-regular,
but not conversely.  We show that the product of any two vertex-path-regular
graphs is vertex-path-regular but not conversely, and the iterated product
%2G %4x %2G %4x * * * x %2G%1 is edge-path-regular if and only if %2G%1 is
edge-path-regular.  An interpretation of path-regular graphs is given regarding
the efficient design of concurrent communication networks.
.skip

%3AIM-337 (STAN-CS-80-808):%1
.once preface 0
@%2Basic Research in Artificial Intelligence and Foundations of Programming%1
by John McCarthy (Principal Investigator), Thomas Binford, David Luckham,
Zohar Manna, Richard Weyhrauch (Associate Investigators)
(75 pages, May 1980)

@Recent research results are reviewed in the areas of formal reasoning,
mathematical theory of computation, program verification, and image 
understanding.
.skip

%3AIM-338 (STAN-CS-80-809):%1
.once preface 0
@%2An Extention of Screw Theory and its Application to the Automation of
Industrial Assemblies%1 by Jorgan S. Ohwovoriole (Thesis, 186 pages, April 1980)

@Interest in mathematical models that adequately predict what happens in the
process of assembling industrial parts has heightened in recent times.  This is
a result of the desire to automate the assembly process.  Up to this point there
has not been much success in deriving adequate mathematical models of the assembly
process.

@This thesis is an attempt to develop mathematical models of parts assembly.
Assembly involves motion of bodies which generally contact each other during
the process.  Hence, we study the kinematics of the relative motion of contacting
bodies.

@Basic to the theory of assembly is the classical theory of screws which,
however, required substantial extensions for this application.  The thesis begins
with a review of basic screw theory, including line geometry and reciprocal screw
systems, and new and more general derivations of some of these screw systems.
We then extend the screw theory by introducing such concepts as "repelling" and
"contrary" screw pairs, and "total freedom."

@Finally, we give a method of characterizing assemblies of industrial parts.
Using the extended screw theory, we then analyze the "general peg-in-hole assembly"
and subsequently give a mathematical description of this particular assembly.
.skip

%3STAN-CS-80-810:%1
.once preface 0
@%2Lower Bounds for algebraic Decision Trees%1 by
J. Michael Steele and Andrew C. Yao
(12 pages, July 1980)

@A topological method is given for obtaining lower bounds for the height of
algebraic decision trees.  The method is applied to the knapsack problem where
a %6W%2n↑2)%1 bound is obtained for trees with bounded-degree polynomial tests,
thus extending the Dobkin-Lipton result for linear trees.  Applications to the
convex hull problem and the distinct element problem are also indcated.  Some
open problems are discussed.
.skip

%3PVG-18 (STAN-CS-80-811):%1
.once preface 0
@%2An Extended Semantic Definition of Pascal for Proving the Absence of
Common Runtime Errors%1 by Steven M. German 
(57 pages, June 1980)

@We present an axiomatic definition of Pascal which is the logical basis of the
Runcheck system, a working verifier for proving the absence of runtime errors
such as arithmetic overflow, array subscripting out range, and accessing an
uninitialized variable.  Such errors cannot be detected at compile time by
most compilers.  Because the occurrence of a runtime error may depend on the
values of data supplied to a program, techniques for assuring the absence of
errors must be based on program specifications.  Runchck accepts Pascal programs
documented with assertions, and proves that the specifications are consistent
with the program and that no runtime errors can occur.  Our axiomatic definition
is similar to Hoare's axiom system, but it takes into account certain restrictions
that have not been considered in previous definitions.  For instance, our
definition accurately models uninitialized variables, and requires a variable to
have a well defined value before it can be accessed.  The logical problems of
introducing the concept of uninitialized variables are discussed.  Our definition
of expression evaluation deals more fully with function calls than previous
axiomatic definitions.

@Some generalizations of our semantics are presented, including a new method of
verifying programs with procedure and function parameters.  Our semantics can
be easily adopted to similar languages, such as ADA.

@One of the main potential problems for the user of a verifier is the need to
write detailed, repetitious assertions.  We develop some simple logical properties
of our definition which are exploited by Runcheck to reduce the need for such
detailed assertions.
.skip

%3HPP-80-14 (STAN-CS-80-812):%1
.once preface 0
@%2Knowledge Engineering:  The Applied Side of Artificial Intelligence%1
by Edward A. Feigenbaum (14 pages, ? 1980)

@Expert System research is an emerging area of computer science that
exploits the capabilities of computers for symbolic manipulation and
inference to solve complex and difficult reasoning problems at the
level of performance of human experts.  The methods of this area are
designed to acquire and represent both the formal and the informal
knowledge that experts hold about the tasks of their disciplin.
Numerous applications to science, engineering, and medicine have been
accomplished.  Expert System projects represent applied artificial
intelligence research, though they also make salient numerous
fundamental research issues in the acquisition, representation, and
utilization of knowledge by computer programs.  Knowledge engineering
approaches promise significant cost savings in certain applications;
intelligent computer-based aids for practitioners in fields whose
knowledge is primarily nonmathematical; and the elucidation of the
heuristic knowledge of experts -- the largely private knowledge of
practice.  There are major problems of knowledge engineering
including the shortage of adequate computer equipment, the shortage
of trained specialists in applied artificial intelligence, the
scientific base for adequate knowledge acquisition, and the lack of
sustained funding.
.skip

%3AIM-340 (STAN-CS-80-813):%1
.once preface 0
@%2Obstacle Avoidance and Navigation in the Real World
by a Seeing Robot Rover}%1
by Hans Peter Moravec
(Thesis, 174 pages, September 1980)

@The Stanford AI lab cart is a card-table sized mobile robot
controlled remotely through a radio link, and equipped with a TV camera
and transmitter. A computer has been programmed to drive the cart through
cluttered indoor and outdoor spaces, gaining its knowledge about the world
entirely from images broadcast by the onboard TV system.

@The cart determines the three dimensional location of objects around
it, and its own motion among them, by noting their apparent relative
shifts in successive images obtained from the moving TV camera. It
maintains a model of the location of the ground, and registers objects it
has seen as potential obstacles if they are sufficiently above the surface,
but not too high. It plans a path to a user-specified destination which
avoids these obstructions. This plan is changed as the moving cart
perceives new obstacles on its journey.

@The system is moderately reliable, but very slow. The cart moves
about one meter every ten to fifteen minutes, in lurches.  After rolling a
meter, it stops, takes some pictures and computes for a long
time. Then it plans a new path, and executes a little of it, and pauses
again.

@The program has successfully driven the cart through several 20
meter indoor courses (each taking about five hours) complex enough to
necessitate three or four avoiding swerves. A less sucessful outdoor run,
in which the cart swerved around two obstacles but collided with a third,
was also done. Harsh lighting (very bright surfaces next to very dark
shadows) resulting in poor pictures, and movement of shadows during the
cart's creeping progress, were major reasons for the poorer outdoor
performance. These obstacle runs have been filmed (minus the very dull
pauses).