{
    "name": "x2",
    "result_type": "RevCTMC[a]",
    "constraints": [ "Doublets[a,b]" ],
    "title": "Rate matrix on doublets constructed from nucleotide rates",
    "call": "SModel.Doublets.x2[submodel,a]",
    "args": [
        {
            "arg_name": "submodel",
            "arg_type": "RevCTMC[b]",
            "alphabet": "getNucleotides[@a]",
	    "description": "Nucleotide rates"
        },
        {
            "arg_name": "a",
            "arg_type": "a",
            "default_value": "getAlphabet",
	    "description": "The Triplets alphabet"
        }
    ],
    "description":"Rate matrix on doublets, constructed from a rate matrix on nucleotides.\n\nThus function can be used to build up doublet models incrementally.",
    "examples": ["f81+x2","gtr+x2"],
    "see": ["x2_sym"]
}
