Phase extension by combined entropy maximization and solvent flattening

An efficient algorithm is described for finding the maximum entropy density distribution under the constraint that (Σ |F|cos (2πh . r- φ)), where the sum is over a subset of reflections whose phase has been determined, is constant. This algorithm is combined with solvent flattening in a procedure for extending phases to higher resolution. A test of the procedure on the structure of ribonuclease A and its application to the determination of two previously unknown structures are discussed.