I’m trying to run ACADOS on a big problem (135 states, 29 controls). One of the issues I came across is the amount of RAM (15 go) necessary to create the graph with an ERK integrator (the compilation line just before the optimization starts). As I am also working with CASADI and IPOPT, I identified that this comes from the fact that the graph is built in SX, whereas it takes way less memory in MX (1/2 go, exactly same problem with CASADI and IPOPT).
I tried to change the integrator because my ODEs are stiff. When I switched to IRK, the amount of RAM used by ACADOS dropped by about 10 times ! So my question is, by pure curiosity, why is that ?!