On Sun, Sep 06 2015, Pรกll Haraldsson <[email protected]> wrote:
> On Friday, August 28, 2015 at 10:28:39 AM UTC, Andreas Lobinger wrote: >> >> >>> that is the right thing. I wander what MATLAB does, since all numbers(?) >>> are stored as complex. 0im special cased? >>> >> >> yes. Only real part is compared, if you need abs(a) > abs(b) or similar. >> > > I wander, since MATLAB compares/orders complex numbers, if Julia should too. > > > http://www.cut-the-knot.org/do_you_know/complex_compare.shtml > "It's actually possible to define the relationship "<" between complex > numbers. [..] Still it's not very useful. To see what the problem is let's > turn to the multiplication." > > > It seems for sorting/datagrids, etc. (DataFrames.jl) you might want this. > > > Does it lead to something very bad? Would if be helpful to special-case > then only sort! and not isless in general? Your problem --- the problem with this whole thread --- is that you don't have a specific application or question in mind; and thus the whole conversation is idle, aimless speculation. You can always define a total order on complex numbers etc, in fact you can define many; take any function f:C->R and define a < b iff f(a) < f(b) (lexicographic orders are another possibility that cannot be defined this way). The question is whether a particular order makes sense, but to answer that you need an application. Particular choices of f make sense for particular applications. Not imposing any particular order for complex numbers etc is a wise design choice, since there is no order that is generally used. Best, Tamas
