Top panel: the lensed arcs (θ map) originated from three sources in the background (not shown in the figure). The total number of pixels forming the arcs is N_θ = 288. Bottom panel: shear field derived from the lens and used for the weak lensing computation. The inner points have been removed to mimic the contamination from cluster member galaxies. Total number of shear points is N_shear = 1301, needed to set the dimension of the lensing matrix. All points have a Gaussian noise of 30%.