Why return “1/(1+exp(-t))” in the ffm_predict.cpp ?

[zceng]

I'm confused about the last line of "ffm_predict.cpp":

ffm_float ffm_predict(ffm_node *begin, ffm_node *end, ffm_model &model) {
    ffm_float r = 1;
    if(model.normalization) {
        r = 0;
        for(ffm_node *N = begin; N != end; N++)
            r += N->v*N->v; 
        r = 1/r;
    }
    ffm_float t = wTx(begin, end, r, model);
    return 1/(1+exp(-t));
}

After reading the paper, "Field-aware Factorization Machines for CTR Prediction" , I think the predict value is the variable "t" , but the return of this function is "1/(1+expp(-t))" . Could you answer my doubt ?