Data layout

All data with multi index are stored plain, e.g. $\hat f_{\mbox{\boldmath\scriptsize {${k}$}}}$ in my_plan.f_hat[ $k_{\text{\tiny $\Pi$}}$], where the plain index again is given by $k_{\text{\tiny $\Pi$}}:=\sum_{t=0}^{d-1} (k_t+\frac{N_t}{2}) \prod_{t'=t+1}^{d-1} N_{t'}$ and the knots $\left(\mbox{\boldmath {${x}$}}_j\right)_t$ in my_plan.x[$dj+t$].