# CARMA OANT Seminar

## 3:00 pm

## Monday, 9^{th} Dec 2013

**V205, Mathematics Building**

# Prof Robert Corless

(University of Western Ontario)
*High-order, high-accuracy solution of a nonlinear PDE arising in a two-dimensional heat transfer model*

A classical nonlinear PDE used for modelling heat transfer between concentric cylinders by fluid convection and also for modelling porous flow can be solved by hand using a low-order perturbation method. Extending this solution to higher order using computer algebra is surprisingly hard owing to exponential growth in the size of the series terms, naively computed. In the mid-1990's, so-called "Large Expression Management" tools were invented to allow construction and use of so-called "computation sequences" or "straight-line programs" to extend the solution to 11th order. The cost of the method was O(N^8) in memory, high but not exponential.

Twenty years of doubling of computer power allows this method to get 15 terms. A new method, which reduces the memory cost to O(N^4), allows us to compute to N=30. At this order, singularities can reliably be detected using the quotient-difference algorithm. This allows confident investigation of the solutions, for different values of the Prandtl number.

This work is joint with Yiming Zhang (PhD Oct 2013).