ei_1.m

H. Yang, A.P. Petropulu, X. Yang and T. Camp, ?ALLIANCES with Optimal Relay Selection,"IEEE Trans. o

%ei_1(a): manually integrating int(e^(-t)/t, a,inf);
function eival=ei_1(a)

if a <=0 
    eival =0;
    EXCEPTION= 'IN EI_1() A<0' 
    return;
end% not the case
if a >=1 
    eival = 0.22;
    EXCEPTION= 'IN EI_1() A>1' 
    return;
end% value when a=1; our case is 0<a<1 since a=1/snr
eival=0;
%datestr(now)
stepp=(1-a)/1e5;
for ii=a:stepp:1
    eival=eival+stepp*exp(-ii)/ii;
end
eival=eival+0.22;