Identifying Implementation Bugs in Machine Learning based Image Classifiers using Metamorphic Testing

We have recently witnessed tremendous success of Machine Learning (ML) in practical applications. Computer vision, speech recognition and language translation have all seen a near human level performance. We expect, in the near future, most business applications will have some form of ML. However, testing such applications is extremely challenging and would be very expensive if we follow today's methodologies. In this work, we present an articulation of the challenges in testing ML based applications. We then present our solution approach, based on the concept of Metamorphic Testing, which aims to identify implementation bugs in ML based image classifiers. We have developed metamorphic relations for an application based on Support Vector Machine and a Deep Learning based application. Empirical validation showed that our approach was able to catch 71% of the implementation bugs in the ML applications.Comment: Published at 27th ACM SIGSOFT International Symposium on Software Testing and Analysis (ISSTA 2018

Bubble propagation through viscoplastic fluids

In this thesis we consider the propagation of an air bubble in a cylindrical column filled with a viscoplastic fluid. Because of the yield stress of the fluid, it is possible that a bubble will remain trapped in the fluid indefinitely. We restrict our focus to the case of slow moving or near-stopped bubbles. Using the Herschel-Bulkley constitutive equation to model our viscoplastic fluid, we develop a general variational inequality for our problem. This inequality leads to a stress minimization principle for the solution velocity field. We are also able to prove a stress maximization principle for the solution stress field. Using these two principles we develop three stopping conditions. For a given bubble we can calculate, from our stopping conditions, a critical Bingham number above which the bubble will not move. The first stopping condition is applicable to arbitrary axisymmetric bubbles. It is strongly dependent on the bubble length as well as the general shape of the bubble. The second stopping condition allows us to use existing solutions of simpler problems to calculate additional stopping conditions. We illustrate this second stopping condition using the example of a spherical bubble. The third stopping condition applies to long cylindrical bubbles and is dependent on the radius of the bubble. In addition to our stopping conditions, we determine how the physical parameters of the problem affect the rise velocity of the bubble. We also conduct a set of experiments using a series of six different Carbopol solutions. From the experiments we examine the dependence of the bubble propagation velocity on the fluid parameters and compare this to our analytic results. We find that there is an interesting discrepancy for low modified Reynolds number flows wherein the bubble velocity increases with a decrease in the modified Reynolds numbers. We also compare our three stopping conditions with the data. It appears that all the stopping conditions seem to be valid for the range of bubbles examined despite the fact that when applying the second and third stopping conditions most bubble shapes are not well approximated by a sphere or a cylinder.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Behaviour of a conducting drop in a viscous fluid subject to an electric field

The slow deformation of a conducting drop surrounded by a viscous insulating fluid subject to a uniform electric field is considered. Two analytic models are presented for inviscid drops. The first makes use of a time-evolving spheroidal shape along with an energy balance to determine the drop behaviour. For fields below a critical value there exist equilibrium shapes. In this case, the evolution of the drop to the equilibrium shape is obtained. Above the critical value no equilibrium shapes exist and the drop has a period of slow elongation before undergoing rapid expansion. The spheroidal model is shown to be accurate up to aspect ratios of about 5. The second model uses slenderbody theory to model the drop behaviour. A similarity solution, exhibiting a finite-time singularity is obtained. Finally, detailed numerical computations, based on a boundary integral formulation, are presented for inviscid and viscous drops. The deformation of the drop right up to breakup is obtained. The type of breakup seen depends on the viscosity ratio of the drop to the surrounding fluid, and on the electric field strength. The different types of breakup seen are small droplets being emitted from the ends of the drop with a charge greater than the Rayleigh limit, the formation of what appear to be conical ends with the subsequent ejection of thin jet-like structures, or the formation of thin jet-like structures without the conical ends. Also, local analytic solutions that allow for a conical end are derived. However, none of the analytic solutions seem to correspond well with the numerical results. Finally, the behaviour of the drop near the critical electric field strength is examined in detail and time scales for the drop evolution are determined.EThOS - Electronic Theses Online ServiceNatural Sciences and Engineering Council of CanadaGBUnited Kingdo