  We propose and experimentally verify a method to program the effective
transmission matrix of general multiport linear optical circuits in random
multiple-scattering materials by phase modulation of incident wavefronts. We
demonstrate the power of our method by programming linear optical circuits in
white paint layers with 2 inputs and 2 outputs, and 2 inputs and 3 outputs.
Using interferometric techniques we verify our ability to program any desired
phase relation between the outputs. The method works in a deterministic manner
and can be directly applied to existing wavefront-shaping setups without the
need of measuring a transmission matrix or to rely on sensitive interference
measurements.
