I'm not sure giving an array of indices will work. so what I want is

qul = idx    val       Edotu = idx  val
       6     0.5                6    2
       6     0.5                7    0.1
       7     1.0

and then $$ q_{ul} \times \dot E_u $$ =

idx   val
 6     1
 6     1
 7     0.1