Hi, I have skimmed over the new proto library a few times now. I am kind of excited about a clean implementation of ET. I have used blitz++ in a project before, but am disappointed, because it breaks unexpectedly in places, where it seems the et engine is just not smart enough, even though the expression makes a lot of sense. I ended up having to handcode a lot of things, avoiding which was the very reason I ever used blitz. So now I am back at hand coing in a new projects, using nothing but a few good iterators. Now with proto I was wondering how hard it would be to build an et engine for array math. Basically I am interested in general tensor notation, and the resulting expressions should be iteratable efficiently. think (advanced example): a_ij = b_i * (c_j - sum(d_ijk, k = [i-1,1]) so there should be math on the indices possible, and I should be able to iterate the expression to avoid direct index lookups wich are expensive with arrays, where indices must be multiplied by strides to get the memory address. other goodies would be optional range checks and the ability to pass subexpressions to template functions. also interesting might be transformations to automatically optimize expressions. a nice start would be maybe something simpler like just a_ij = b_i * (c_j - sum(d_ijk, k) where k is summed fully (over the whole range in d_ijk). can anymone give me an estimate on how hard this would be and where to start? Best Daniel Oberhoff Fraunhofer FIT St. Augustin Birlinghoven