At this point it is important to discuss a challenge that arises when learning the c z 0 (R) surface. In the direct MECI optimization approach used here, the minimizing gradient is separated into two components. The first minimizes the average energy projected onto the seam space, and the second component minimizes a quantity proportional to ∆E 2 , with its minimizing gradient as 2∆E(∇x), where x is the normalized energy difference gradient.