A start node acquires coupled state information indicating a connectibility of nodes from a network. The phantom comprises two concentrically-disposed, fluid-tight, flexible membranes defining a closed space between the walls of the membranes. The evaporator extends over at least part of the wall pertaining to the lower region, and the cooling performance of the evaporator, in its part pertaining to the upper or lower region, is such that the temperature reached in the upper region of the inner chamber is lower than that reached in the lower region. Each syndrome may be produced by applying to the bits vector operations in a vector space.