Everybody: Thank you very much for your advice. I believe that I have gotten the loops working now.
The method conductivity(), 2 million triangles With loops expanded: 25.294999069 seconds (5253831296 bytes With matrix operations: 29.744513256 seconds (6564763296 So now the loops win by about 15% of time consumed. The key was apparently to have every single variable declared. I'm not quite sure how the compiler is able to pursue the tree of interdependent modules to ferret out the types, but I think it must have missed a few (the modules properly declared the types, but I'm not sure if the compiler saw them). Therefore I believe the loops were losing heavily compared to matrix operations. So I went in and declared everything I could get my hands on. That made the loops competitive. The moral of this story is: If you can't or won't declare every single variable, don't do loops. They are likely to be a losing proposition. The updated code is at https://gist.github.com/PetrKryslUCSD/7bd14515e1a853275923 Petr PS: One particular problem was that I was calling the function stored as type Function. Being new to the language, I don't know if I can declare the function to have a type that would indicate the type of the return value. (Is it possible?) Without this information, the compiler is apparently stuck with data whose types need to be determined at runtime. Unfortunately, the compiler does not throw fits when it does not know the type, and then bad things can happen as in the present example where expanding the loops was twice as slow as doing a matrix operation.
