Sum represents a sum of terms. Like any other expression, it inherits all properties of Tensor.
Sum adopts the following convention on its indices: the indices of sum are free sorted indices of its summands:
def t = 'f_ba^c_c + t_ab^d_d'.t println t.indice
Sum sorts its arguments and reduces any equal terms. Additionally, it reduces terms with same tensorial parts as described in Standard form of mathematical expressions.
||returns a sum of elements at specified positions|
||returns a sum with removed elements at specified positions|
def s = 'a + b + c + d + e + f'.t println s.select(2, 3, 5)
println s.remove(2, 3, 5)