static inline MatShape concat(const MatShape& a, const MatShape& b)
{
MatShape c = a;
c.insert(c.end(), b.begin(), b.end());
return c;
}
static inline MatShape shape(int a0, int a1=-1, int a2=-1, int a3=-1)
{
int dims[] = {a0, a1, a2, a3};
MatShape s = shape(dims, 4);
s.erase(std::remove_if(s.begin(), s.end(), is_neg), s.end());
return s;
}