// alpha is the K2=2*K dimensional vector containing the real and imaginary part of \alpha_t
//fktilde contains the quantities 2a/(L*\pi)*(2\gamma_t-1)
void PHI_gVg(double t, double gamma[K2], double tktilde[K]){
int i,i2,i3;
double tmp,tmp2,tmp3,costmp,sintmp;
double re_s=0.0;//re_s contains real part of sum over \alpha_t(k)
double im_s=0.0;//im_s contains imaginary part of sum over \alpha_t(k)
for(i=0;i