Todo List
quadratic (p-o)'S'S(p-o) solve for o, S S is a single scale factor
void grad( array[] $x, array[] $a, int $a_k)
z = (p-o)'S'S(p-o) dz/dp = 2S'S(p-o) z = (s*(px-ox))^2 + (s*(py-oy))^2 dz/dox = -2(s*(px-ox))*s dz/ds = 2*s*[(px-ox)^2 + (py-oy)^2] z = (s*dx)^2 + (s*dy)^2 dz/ds = 2(s*dx)*dx + 2(s*dy)*dy
array[] initial( )
Object[] testdata( )
void val( array[] $x, array[] $a)