This parameter can be used in the very specific problems implying either a cavity defined by CavityRadius, CavityRatio and CavityWidth or a temperature transition defined by TransitionRadius, TransitionRatio and TransitionWidth. It is used to vary the cavity or temperature transition radius with time (this parameter was first introduced to show that a planet locked at a cavity edge is trapped by this latter, since it follows its radial evolution). More precisely, this parameter must be set to the inverse of the timescale over which the cavity radius is doubled with respect to its value at run start (or restart). The cavity radius is an affine function of time. LambdaDoubling defaults to 0, which yields a constant cavity or transition radius.