SparseConcate
int64 ii1(?)
int64 jj1(?)
double vv1(?)
int32 m1()
int32 n1()
int64 ii2(?)
int64 jj2(?)
double vv2(?)
int32 m2()
int32 n2()
bool hcat()
int64 ii(?) -> output
int64 jj(?) -> output
double vv(?) -> output
