# How to handle reductions on interval arrays

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## How to handle reductions on interval arrays

 Hi Oliver, A new week and some new questions! I have almost finished the work on vectorization. The only thing that is left is how to handle ctc_union.m, ctc_intersection.m and fsolve.m. These functions are a bit more complicated however so I will wait a bit with them. Instead I have started to work on folding/reduction functions (Octave seems to use the word reduction in the source code at least). I have implemented support for N-dimensional arrays in sum.m (and also in mpfr_vector_sum_d.cc). In that change there are also some other changes, I have moved all of the vectorization inside the oct-file (yielding about a 2 times speed up) and have slightly modified how it handles empty arrays to be consistent with how the standard sum-function does it. When I were to work on dot.m I realized that Octaves standard implementation is a bit odd. It is inconsistent with both the sum-function and Matlab. See bug #51333, https://savannah.gnu.org/bugs/?51333, on Savannah for more detailed info. I think that the interval package should follow Octave, but in this case Octave is weird. Probably we should wait and see what happens with my bug report. I have also worked on prod.m and while doing that I encountered something which I think is a bug. But I'm not sure so I thought I would ask first. A minimal example is the code > x = infsup (1:4); > i = logical ([0 1 0 0]); > x(i) ans = [2] where everything is as it should. However when I try to put this code inside an interval function, for example testme.m, it does not work. With function testme (arg)   x = infsup (1:4);   i = logical ([0 1 0 0]);   x(i); endfunction we get > testme (infsup ([])) error: x(2): out of bound 1 error: called from     testme at line 7 column 3 It is important that testme.m is inside the @infsup folder, otherwise it seems to work. Do you have any idea of what this is? Best, Joel Dahne
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