[ont.events] U of Toronto Computer Science activities, Oct. 5-9

clarke@utcsri.UUCP (09/29/87)

         (SF = Sandford Fleming Building, 10 King's College Road)
              (GB = Galbraith Building, 35 St. George Street)

SUMMARY:

COMBINATORICS SEMINAR, Monday, October 5, 3 pm  SF1102 -- Irith Hartman:
    "Path Partitions and Independent Sets In Directed Graphs"

COLLOQUIUM, Tuesday, October 6, 11 am, SF1105 -- C. Rackoff:
    "Cryptography: State of the Art"

A.I. SEMINAR, Tuesday, October 6, 2 pm,  GB244 -- Chuck Rich:
    "Bread, Frappe and Cake: A Gourmet's Guide to Automated Deduction"

GRAPHICS SEMINAR, Tuesday, October 6, 3 pm, GB120 -- Philip K. Robertson:
 "Displaying images as surfaces - a new approach to the hidden surface problem"

--------------------

          COMBINATORICS SEMINAR, Monday, October 5, 3 pm  SF1102

                          Professor Irith Hartman
                             Visiting Post-doc
                      Department of Computer Science
                           University of Toronto

                   "Path Partitions and Independent Sets
                           In Directed Graphs"

               COLLOQUIUM, Tuesday, October 6, 11 am, SF1105

                           Professor C. Rackoff
                           University of Toronto

                     "Cryptography: State of the Art"

The only cryptosystems known to be secure, such as the one-time pad, have a
private key as long as the message to be sent.  It is possible (although
unlikely) that every other system is insecure, and it is even plausable
that every currently known system is insecure.  The best that we know how
to do is to construct systems that can be proven to be secure assuming cer-
tain number theory conjectures.  Assuming these conjectures are true, we
cannot only do traditional cryptography, but we can also construct many
wonderful and counterintuitive protocols for other tasks.  For example, I
can prove to you that a mathematical theorem is true, without giving you
any idea of why it is true or any idea of how to prove it.

              A.I. SEMINAR, Tuesday, October 6, 2 pm,  GB244

                           Professor Chuck Rich
                                MIT AI LAB

                        "Bread, Frappe and Cake:
                 A Gourmet's Guide to Automated Deduction"

Cake is the knowledge representation and reasoning system developed as part
of the Programmer's Apprentice project.  Cake can be thought of as an
active database, which performs quick and shallow deductions automatically;
it supports both forward-chaining and backward-chaining reasoning.  The
Cake system has a layered architecture: the kernel of the system, called
Bread (for Basic REAsoning Device), is a truth-maintenance system with
equality and demons.  Built on top of this is Frappe (for FRAmes in a Pro-
Positional Engine), which implements a typed logic with special-purpose
decision procedures for various algebraic properties of operators (such as
commutativity and associativity), sets, partial functions, and structured
objects (frames).  Only the topmost layer of Cake, which implements the
Plan Calculus, is specific to reasoning about programs.  This talk will
describe the architecture and features of Bread, Frappe, and Cake,
including a transcript of a demonstration session.  This is joint work with
Yishai Feldman.


             GRAPHICS SEMINAR, Tuesday, October 6, 3 pm, GB120

                       Professor Philip K. Robertson
                           University of Toronto

              "Displaying images as surfaces - a new approach
                      to the hidden surface problem"

Surface representations allow arbitrarily-valued images (height fields, or
terrain models) to be displayed, analysed and manipulated.  However, con-
ventional parametic and object-oriented graphics techniques are not neces-
sarily well suited to handling image data.  In particular, processes which
involve hidden-surface elimination, such as the generation of 3-D perspec-
tive views or surface shadowing, can incurr substantial computational and
I/O costs. This seminar will show how spatial transformations can reduce
hidden-surface determination to a simple 1-D process, decreasing computa-
tional costs significantly and simplifying data I/O requirements.  The
approach is scan-line in nature, and relies on the separability of
transforms, such as the perspective projection, into 1-D operations per-
formed on scan-rows or scan-columns of the image.  Parallel hardware offers
the potential for extremely rapid operation. The approach has the addi-
tional advantages that it can be implemented in a severely memory-limited
environment, and that it greatly facilitates interpolation, antialiasing
and some physical modelling.  The more general potential of spatial
transformations of this nature in image processing and graphics will also
be discussed.
-- 

Jim Clarke -- Dept. of Computer Science, Univ. of Toronto, Canada M5S 1A4
              (416) 978-4058
{allegra,cornell,decvax,linus,utzoo}!utcsri!clarke