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The squared matrix element Widths implementation parameters C output files Process section Contents

The squared matrix element

double sqme_(int nsub,double * momenta, int * err) returns the numerical value of squared matrix element after summation over out-particle polarizations and averaging over in-particle polarizations. Here nsub is a subprocess number, momenta is an array of particle momenta. The $i^{th}$ Lorentz component of the particle number N corresponds to momenta[4*N+i],
*err is a return parameter which does not equal zero if sqme_ cannot be evaluated.

We assume that the zero Lorentz components of momenta are positive and the sum of incoming particle momenta is equal to the sum of outgoing particle momenta.