A method of signal processing with reduced combinatorial complexity to determine trajectories for evolving physical phenomena associated with obtainable parameters, wherein the trajectories comprise plausible evolutions of the phenomena based on obtained parameters, and associations between phenomena and parameters may be represented within a tree structure having a plurality of nodes, each node representing at least one association between an obtained parameter and a phenomenon, and having at least one of a child or parent relationship with another node, characterised in that the method includes: a1) where it is possible that a given parameter is associated with a given phenomenon, determining how associations between the obtained parameters and that phenomenon affect possible associations between other parameters and phenomena to establish a child node identity based on that determination, a2) ordering a set of given phenomena according to the number of obtained parameters associated to one of said phenomena, such that the phenomenon with the largest intersection of associated parameters with parameters associated to one other phenomenon of said set of given phenomena comes first in a list of sets of given phenomena and associated parameters, b) generating, in the order determined in the previous ordering step, child nodes corresponding to the parameters associated with the respective phenomenon, wherein the child nodes of an earlier generating step in said order represent parent nodes for child nodes of a later generating step, wherein a child node identity indicates parameters which have not yet been assigned in parent nodes of the current node in said tree structure, c) whenever, in the generating step b) a child node identity to be generated is the same as a child node identity which has already been generated, treating those same child node identities for a phenomenon as a single node with multiple parameter relationships corresponding to parameters associated with at least one parent node; and d) representing child nodes with differing identities as separate nodes. a1) where it is possible that a given parameter is associated with a given phenomenon, determining how associations between the obtained parameters and that phenomenon affect possible associations between other parameters and phenomena to establish a child node identity based on that determination, a2) ordering a set of given phenomena according to the number of obtained parameters associated to one of said phenomena, such that the phenomenon with the largest intersection of associated parameters with parameters associated to one other phenomenon of said set of given phenomena comes first in a list of sets of given phenomena and associated parameters, b) generating, in the order determined in the previous ordering step, child nodes corresponding to the parameters associated with the respective phenomenon, wherein the child nodes of an earlier generating step in said order represent parent nodes for child nodes of a later generating step, wherein a child node identity indicates parameters which have not yet been assigned in parent nodes of the current node in said tree structure, c) whenever, in the generating step b) a child node identity to be generated is the same as a child node identity which has already been generated, treating those same child node identities for a phenomenon as a single node with multiple parameter relationships corresponding to parameters associated with at least one parent node; and d) representing child nodes with differing identities as separate nodes.