65 const size_t size = this->size();
66 if(firstDerivative.size() != size)
67 firstDerivative.resize(size, 0.0);
69 firstDerivative[0] = ((*this)[1] - (*this)[0]) / hz;
70 for(
unsigned int i = 1; i + 1 < size; ++i)
71 firstDerivative[i] = ((*
this)[i + 1] - (*
this)[i - 1]) / hz;
72 firstDerivative[size - 1] = ((*this)[size - 1] - (*this)[size - 2]) / hz;