  Inverse scattering problems without the phase information arise in imaging of
nanostructures whose sizes are hundreds of nanometers as well as in imaging of
biological cells. The governing equation is the 3-d generalized Helmholtz
equation with the unknown coefficient, which represents the spatially
distributed dielectric constant. It is assumed that only the modulus of the
complex valued wave field is measured on a frequency range. The phase is not
measured. Two rigorous numerical methods are tested and their performances are
compared for realistic ranges of parameters.
