i think i've figured out how to provide extesibility for back ends consider 2 ways 1. let operations recognize supported expressions C = a*A*B + b*C; //C = a * prod (A, B) + b * C //from uBLAS docs when parsing we encounter (a*A)*B and an operation yells "i know it! i know it! that's a <some particular operation>! i can do it!" and then introduces compatible templates if needed and fall to back end 2. let evaluating function decide evaluating function recieves an expression which is an AST then it recognizes (or not) particular patterns, introduces templates where appropriate and fall to back end hower this technique is better i suppose because it allows to recognize patterns descently consider C = a*A*B + b*C*D; a pattern is recognized (<a>*<A>*<B> + <1.>*<b*C*D>) and now we need to introduce a temporary for 'b*C*D' and a new pattern appears (scaled product of matrices in this case) either of cases need some templates specializations but in a slightly different manner (i didn't think so for which is harder to implement) -- Pavel