Category: Uncategorized

Flying Math: Bees Solve Traveling Salesman Problem

Bumblebees foraging in flowers for nectar are like salesmen traveling between towns: Both seek the optimal route to minimize their travel costs. Mathematicians call this the “traveling salesman problem,” in which scientists try to calculate the shortest possible route given a theoretical arrangement of cities. Bumblebees, however, take the brute-force approach: For them, it’s simply a matter of experience, plus trial and error, as reported in this Wired article.

A System-based Approach to Spares Management

The traditional approach to inventory provisioning sets all spares requirements to a level that meets an item’s performance measure, such as a stock-out protection level, a fill rate, a mission critical rate, or a confidence level. Such an approach cannot explicitly consider the overall performance of the system, nor can it be constrained to a set total cost for the spares mix.

However, a spares’ benefit should be measured in terms of the projected increase in system availability by adding that spare to the inventory. The system-based inventory provisioning approach is significantly different from the traditional item approach for generating spares requirements, which treats all items the same. In system-based inventory provisioning, spares can then be ranked in terms of benefit, then divided by cost as a measure of the desirability of adding them to the inventory.

The problem then is to answer the question “What mix of spare parts is required to keep the system at some level of operational performance for a specific scenario?”. An optimal solution in this case means a solution in which no other mix of spares can provide a greater system availability for the same cost, or the same system availability for less cost (within the scope of the model assumptions and data). Thus, there exists not just one solution, but a set of solutions that represent different trade-off between system availability and cost.

An example of system-based inventory provisioning is the work on the Aircraft Sustainability Model from the Logistics Management Institute which is a mathematical statistical model used by the United States Air Force to computes optimal spares mixed to support a wide range of possible scenarios. Another example is the D-SIMSPAIR product from D-SIMLAB Technologies which uses simulation-based optimization to compute optimal mix of aerospace rotables for maintenance contracts.

Related Links:

 

Unit Testing: Is There Really Any Debate Any Longer?

On a panel several years ago, Dr. Dobbs’s editor-in-chief Andrew Binstock was asked what was the greatest benefit that Agile had delivered to him personally. It took him no time to respond “unit testing.”

While this answer is not historically accurate — unit testing precedes the Agile movement — it’s clear that the Agile exponents made it a widespread practice. In large part, because of Kent Beck’s lapidary JUnit implementation, which has been widely copied to most major languages.

The specific benefit Andrew — and many other developers — have enjoyed is quite simply less time spent in the debugger. Today he writes code and then he writes unit tests that exercise the edge cases and one or two main cases. Right away, Andrew can tell if he missed something obvious or if his implementation has a slight burble that mishandles cases he expected to flow through easily.

Read the rest of this artcile here.