A lens-mapping algorithm for weak lensing

We develop an algorithm for the reconstruction of the two-dimensional mass distribution of a gravitational lens from the observable distortion of back ground galaxies. From the measured reduced shear, the lens mapping is obtai ned, from which a mass distribution is derived. This is unlike other method s where the convergence kappa is directly obtained. We show that this metho d works best for subcritical lenses but can be applied to a critical lens a way from the critical lines. For finite fields, the usual mass-sheet degene racy is shown to exist in this method. We show that the algorithm reproduce s the mass distribution within acceptable limits when applied to simulated noisy data.