An underflow-induced graphics failure solved by SLI arithmetic

Floating-point underflow is often regarded as either harmless or as an indication that the computational algorithm is in need of scaling. A counterexample to this view is given of a function for which contour plotting is difficult due to floating-point underflow. The function arose as an asymptotic solution to a model problem in turbulent combustion in which two chemical species (fuel and oxidizer) mix and react in a vortex field. Scaling is not a viable option because of extreme sensitivity to a small physical parameter. Standard graphics software packages produce erroneous contours without any indication of difficulty. This example provides support for considering symmetric level-index arithmetic, a new form of computer arithmetic which is immune to underflow and overflow.<>