# Leslie Valiant

# Leslie Valiant

- T. Jefferson Coolidge Professor of Computer Science and Applied Mathematics

### Profile

Computer science encompasses the study of both artificial as well as natural phenomena. The former concern artificially created devices such as computers. The latter relate to the many step-by-step, or computational, processes found in nature such as in the brain or in the course of biological evolution. In most areas, whether natural or artificial, the ultimate limitations of such processes are as yet not well understood. The potential of computing devices may be currently far from being fully realized, while fundamental quantitative questions in neuroscience and evolution remain unanswered. Professor Valiant's current research focuses on a number of such basic questions.

The majority of computational problems, including those with explicit mathematical characterizations such as the NP-complete problems, fall within the category of those for which the question of how best to compute them is little understood. These core problems of complexity theory remain the most fundamental mathematical challenges of computer science. They are related to foundational questions in quantum physics, most notably through polynomial time versions of the Turing hypothesis. Professor Valiant has proposed algebraic formulations of these questions, and is currently pursuing the holographic approach.

In computer systems major conceptual challenges remain in controlling, load-balancing and programming large parallel systems, whether they be multicore devices on a chip or highly distributed systems. Professor Valiant's most recent interest in this area concerns the problem of how to design algorithms for multi-core devices that are portable, and run efficiently on wide classes of architectural designs with widely varying performance characteristics.

A fundamental question for artificial intelligence is to characterize the computational building blocks that are necessary for cognition. A specific challenge is to build on the success of machine learning so as to cover broader issues in intelligence. This requires, in particular a reconciliation between two contradictory characteristics--the apparent logical nature of reasoning and the statistical nature of learning. Professor Valiant has developed a formal system, called robust logics, that aims to achieve such a reconciliation.

In neuroscience a widely open problem remains how the weak model of computation that cortex apparently offers can support cognitive computation at all. Professor Valiant has been working on showing how broad sets of primitive operations can be computed robustly and on a significant scale even on such a weak model.

A challenge in a different direction is understanding how Darwinian evolution can evolve complex mechanisms in the numbers of generations and with population sizes that have apparently been available on earth. Darwin's notions of variation and selection are computational notions and offer a very direct challenge for quantitative analysis by the methods of computer science. What is sought is a quantitative understanding of the possibilities and limitations of the basic Darwinian process.

### Positions & Employment

Harvard School of Engineering and Applied Sciences

- 1982-Present. Since 2001: T. Jefferson Coolidge Professor of Computer Science and Applied Mathematics

- 1977-1982: Faculty Member

- 1974-1976: Faculty Member

- 1973-1974: Visiting Faculty Member

### Other Experience & Professional Membership

- Fellow, Royal Society (London)
- Fellow, American Association for Artificial Intelligence
- Member, National Academy of Sciences

### Honors

- Turing Award, 2010
- European Association for Theoretical Computer Science Award, 2008
- Knuth Prize, 1997
- Nevanlinna Prize, 1986