Plan Recognition in a Programmer's Apprentice

This report describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the Laboratory's artificial intelligence research is provided in part by the Advanced Research Projects Agency of the Department of Defense under the Office of Naval Research contract N00014-75-C-0643.Brief Statement of the Problem: Stated most generally, the proposed research is concerned with understanding and representing the teleological structure of engineered devices. More specifically, I propose to study the teleological structure of computer programs written in LISP which perform a wide range of non-numerical computations. The major theoretical goal of the research is to further develop a formal representation for teleological structure, called plans, which will facilitate both the abstract description of particular programs, and the compilation of a library of programming expertise in the domain of non-numerical computation. Adequacy of the theory will be demonstrated by implementing a system (to eventually become part of a LISP Programmer's Apprentice) which will be able to recognize various plans in LISP programs written by human programmers and thereby generate cogent explanations of how the programs work, including the detection of some programming errors.MIT Artificial Intelligence Laboratory Department of Defense Advanced Research Projects Agenc

Principles of Knowledge Representation and Reasoning in the FRAPPE System

The purpose of this paper is to elucidate the following four important architectural principles of knowledge representation and reasoning with the example of an implemented system: limited reasoning, truth maintenance, hybrid architecture, and many sorted logic.MIT Artificial Intelligence Laborator

Understanding LISP Programs: Towards a Programmer's Apprentice

Work reported herein was conducted at the Artificial Intelligence Laboratory, a Massachusetts Institute of Technology research program supported in part by the Advanced Research Projects Agency of the Department of Defense and monitored by the Office of Naval Research under Contract Number N00014-70-A-0362-0005.Several attempts have been made to produce tools which will help the programmer of complex computer systems. A new approach is proposed which integrates the programmer's intentions, the program code, and the comments, by relating them to a knowledge base of programming techniques. Our research will extend the work of Sussman, Goldstein, and Hewitt on program description and annotation. A prototype system will be implemented which answers questions and detects bug in simple LISP programs.MIT Artificial Intelligence Laborator

The Interaction Between Truth Maintenance, Equality, and Pattern-Directed Invocation: Issues of Completeness and Efficiency

We have implemented a reasoning system, called BREAD, which includes truth maintenance, equality, and pattern-directed invocation. This paper reports on the solution of two technical problems arising out of the interaction between these mechanisms. The first result is an algorithm which ensures the completeness of pattern-directed invocation with respect to equality. The second result is an algorithm which reduces a class of redundant proofs.MIT Artificial Intelligence Laborator

The Disciplined Use of Simplifying Assumptions

Submitted to the ACM SIGSOFT Second Software Engineering Symposium: Workshop on Rapid Prototyping. Columbia, Maryland, April 19-21, 1982.Simplifying assumptions — everyone uses them but no one's programming tool explicitly supports them. In programming, as in other kinds of engineering design, simplifying assumptions are an important method for dealing with complexity. Given a complex programming problem, expert programmers typically choose simplifying assumptions which, though false, allow them to arrive rapidly at a program which addresses the important features of the problem without being distracted by all of its details. The simplifying assumptions are then incrementally retracted with corresponding modifications to the initial program. This methodology is particularly applicable to rapid prototyping because the main questions of interest can often be answered using only the initial program. Simplifying assumptions can easily be misused. In order to use them effectively two key issues must be addressed. First, simplifying assumptions should be chosen which simplify the design problems significantly without changing the essential character of the program which needs to be implemented. Second, the designer must keep track of all the assumptions he is making so that he can later retract them in an orderly manner. By explicitly dealing with these issues, a programming assistant system could directly support the use of simplifying assumptions as a disciplined part of the software development process.MIT Artificial Intelligence Laborator

A Detection of Gas Associated with the M 31 Stellar Stream

Detailed studies of stellar populations in the halos of the Milky Way and the Andromeda (M 31) galaxies have shown increasing numbers of tidal streams and dwarf galaxies, attesting to a complicated and on-going process of hierarchical structure formation. The most prominent feature in the halo of M 31 is the Giant Stellar Stream, a structure ~4.5 degrees in extent along the sky, which is close to, but not coincident with the galaxy's minor axis. The stars that make up this stream are kinematically and chemically distinct from the other stars in the halo. Here, we present HST/COS high-resolution ultraviolet absorption spectra of three Active Galactic Nuclei sight lines which probe the M 31 halo, including one that samples gas in the main southwestern portion of the Giant Stream. We see two clear absorption components in many metal species at velocities typical of the M 31 halo and a third, blue-shifted component which arises in the stream. Photoionization modeling of the column density ratios in the different components shows gas in an ionization state typical of that seen in other galaxy halo environments and suggests solar to slightly super-solar metallicity, consistent with previous findings from stellar spectroscopy.Comment: 10 pages, 5 figures, accepted for publication in the Astrophysical Journa

Formalizing Reusable Software Components

This paper has been accepted by the ITT Workshop on Reusability in Programming, Newport RI, September 7-9, 1983.There has been a long-standing desire in computer science for a way of collecting and using libraries of standard software components. Unfortunately, there has been only limited success in actually doing this. We believe that the lack of success stems not from any resistance to the idea, nor from any lack of trying, but rather from the difficulty of choosing an appropriate formalism for representing components. In this paper we define five desiderata for a good formalization of reusable software components and discuss many of the formalisms which have been used for representing components in light of these desiderata. We then briefly describe a formalism we are developing — the Plan Calculus — which seeks to satisfy these desiderata by combining together the best features of prior formalisms.MIT Artificial Intelligence Laborator

Time-stepping approach for solving upper-bound problems: Application to two-dimensional Rayleigh-Benard convection

An alternative computational procedure for numerically solving a class of variational problems arising from rigorous upper-bound analysis of forced-dissipative infinite-dimensional nonlinear dynamical systems, including the Navier-Stokes and Oberbeck-Boussinesq equations, is analyzed and applied to Rayleigh-Benard convection. A proof that the only steady state to which this numerical algorithm can converge is the required global optimal of the relevant variational problem is given for three canonical flow configurations. In contrast with most other numerical schemes for computing the optimal bounds on transported quantities (e.g., heat or momentum) within the "background field" variational framework, which employ variants of Newton's method and hence require very accurate initial iterates, the new computational method is easy to implement and, crucially, does not require numerical continuation. The algorithm is used to determine the optimal background-method bound on the heat transport enhancement factor, i.e., the Nusselt number (Nu), as a function of the Rayleigh number (Ra), Prandtl number (Pr), and domain aspect ratio L in two-dimensional Rayleigh-Benard convection between stress-free isothermal boundaries (Rayleigh's original 1916 model of convection). The result of the computation is significant because analyses, laboratory experiments, and numerical simulations have suggested a range of exponents alpha and beta in the presumed Nu similar to (PrRa beta)-Ra-alpha scaling relation. The computations clearly show that for Ra <= 10(10) at fixed L = 2 root 2, Nu <= 0.106Pr(0)Ra(5/12), which indicates that molecular transport cannot generally be neglected in the "ultimate" high-Ra regime.NSF DMS-0928098 DMS-1515161 DMS-0927587 PHY-1205219Simons FoundationNSFONRInstitute for Computational Engineering and Sciences (ICES

Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33

We present far-ultraviolet (far-UV) images of the rich galaxy cluster ZwCl1358.1+6245, taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope (HST). When combined with archival HST observations, our data provide a measurement of the UV-to-optical flux ratio in 8 early-type galaxies at z=0.33. Because the UV flux originates in a population of evolved, hot, horizontal branch (HB) stars, this ratio is potentially one of the most sensitive tracers of age in old populations -- it is expected to fade rapidly with lookback time. We find that the UV emission in these galaxies, at a lookback time of 3.9 Gyr, is significantly weaker than it is in the current epoch, yet similar to that in galaxies at a lookback time of 5.6 Gyr. Taken at face value, these measurements imply different formation epochs for the massive ellipticals in these clusters, but an alternative explanation is a "floor" in the UV emission due to a dispersion in the parameters that govern HB morphology.Comment: 4 pages, Latex. 2 figures. Uses corrected version of emulateapj.sty and apjfonts.sty (included). Accepted for publication in ApJ Letter