Question

I’m writing a small and inadequate linear algebra library in C++ for a project (I’m sorry). I’m implementing matrices and operations using double precision numbers. I’m doing right? Should I implement a template class instead? Is there a more precise type around?

Answer 1

I’ve written a C++ linear algebra library using templates. My thought was that we might want to use complex numbers or extended precision numbers some day. That was maybe seven years ago, and we haven’t done it yet. We almost always use doubles as the template type, and we have typedefs to make that easy.

A few times we’ve gone the other way, using types smaller than a double. For example, we’ve used float rather than double in a memory-bound application described here. But 99.9 percent of the time we use doubles.

If you do use a template argument, watch out for using an integer type but implicitly requiring a floating point type. For example, say you have a matrix whose entries are all integers and so you use a matrix<int> class. But then you pass that to a linear solver. Now your arithmetic is done using integer division, and your results are wrong. (I’ve done that!)