Matching variables - for a pair of articles with a common author name (matching on last-a and first)
x1 = 1 if mid1 = mid2, 0 otherwise
x2 = 1 if last-i1 = last-i2 ~= last-a, 0 otherwise
x3 = |co-auth1 AND co-auth2|: {0,1,2,ɮ}
x4 = |title1 AND title2|: {0,1,2,ɮ}
x5 = |affl1 AND affl2|: {0,1,2,ɮ}
x6 = |geo(affl1) AND geo(affl2)|: {0,1,2,ɮ}
x7 = |mesh1 AND mesh2|: {0,1,2,ɮ}
x8 = 1 if type1 = type2 ~= journal article, 0 otherwise
x9 = 1 if jrnl1 = jrnl2, 0 otherwise
x10 = 1 if lang1 = lang2 ~= english, 0 otherwise
x11 = - frq: {-2, -3, …,}