“…We note that in our setting we assume to have observations of z δ ∈ L 2 ( ), ∇z δ ∈ (L 2 ( )) d for the solution u and its gradient, respectively. Such assumptions have been used by many authors, e.g., Acar [1], Banks and Kunisch [4], Chan and Tai [7,8], Chavent [9], Chavent and Kunisch [10], Chen and Zou [11], Ito and Kunisch [20,21], Ito, Kroller and Kunisch [23], Keung and Zou [25], Knowles et al [28,29], Kohn and Lowe [31], Vainikko [37,38], Vainikko and Kunisch [39], Zou [41]. In practice, the observation is measured at certain points and we need to interpolate the point observations to get distributed observations.…”