  We present a finite-difference method for the topology optimization of
permanent magnets that is based on the FFT accelerated computation of the
stray-field. The presented method employs the density approach for topology
optimization and uses an adjoint method for the gradient computation.
Comparsion to various state-of-the-art finite-element implementations shows a
superior performance and accuracy. Moreover, the presented method is very
flexible and easy to implement due to various preexisting FFT stray-field
implementations that can be used.
