But if it does not makes sense from your point to give a full matrix, why does it make more sense to return a diagonal matrix? It is still lots of heap allocated memory. So you replace a large performance trap with a smaller one. What has been gained? We would still have to teach people the eye should not be used because there is a faster alternative.
Am Montag, 29. August 2016 18:04:15 UTC+2 schrieb Chris Rackauckas: > > As Julio asks, why should the default be a dense identity matrix? Who > actually wants to use that? I agree `I` should be in more visible in the > docs and in most cases it's the better option. But if you actually want a > matrix as an array instead of just an operator (this is reasonable, because > maybe you're going to modify it), then a Diagonal matrix is sufficient for > storing any identity matrix and should be the only thing used in most > cases. If you really want a dense matrix from it, you could always call > full(A). But there's almost no reason to have a dense identity matrix, and > so Julia shouldn't be defaulting to it because it's just a performance trap > for new users coming from MATLAB. > > On Monday, August 29, 2016 at 8:31:13 AM UTC-7, Kristoffer Carlsson wrote: >> >> What is the confusion? Use eye(n) if you want a dense identity matrix. >> Use I if you want something that acts like an identity element. Use >> Diagonal(ones(n)) if you want a diagonal identity matrix. I see no reason >> at all why eye should be changed. >> >> On Monday, August 29, 2016 at 4:32:34 PM UTC+2, Chris Rackauckas wrote: >>> >>> But you don't want a sparse matrix. It would not be an efficient way to >>> actually use it since sparse matrices have a bit of overhead due to their >>> table structure. Even better would be a Diagonal since it's just an array >>> with dispatches to act like a diagonal matrix. But best would be to use the >>> UniformScaling operator `I` which acts like eye in cases like A-λI but >>> isn't actually saving a matrix and doesn't actually require iterating over >>> two arrays at once. I think that amount of confusion in this thread is a >>> good indicator that eye should be changed. >>> >>> On Monday, August 29, 2016 at 7:25:49 AM UTC-7, Kristoffer Carlsson >>> wrote: >>>> >>>> You mean a sparse matrix? >>> >>>
