inner product of DD vectors
z = ddip(x,y)
2 column vectors of real DD numbers, of same lengths.
DD number = x'*y
x = ddrand(10,1); y = ddrand(10,1); z = ddip(x,y) z == x' * y sqrt(ddip(x,x)) == norm(x,2)
--> z = ddip(x,y) z = 2.407167425747500363001462552151E0 --> z == x' * y ans = T --> sqrt(ddip(x,x)) == norm(x,2) ans = T