HP 48gII hp 48gII_user's manual_English_E_HDPMSG48E67_V2.pdf - Page 551

Function RRKSTEP This function uses an input list similar to that of function RRK, as well as the tolerance for the solution, a possible step ∆x, and a number (LAST) specifying the last method used in the solution (1, if RKF was used, or 2, if RRK was used). Function RRKSTEP returns the same input list, followed by the tolerance, an estimate of the next step in the independent variable, and the current method (CURRENT) used to arrive at the next step. Thus, the input stack looks as follows: 4: {'x', 'y', 'f(x,y)'} 3: ε 2: ∆x 1: LAST After running this function, the stack will show the lines: 4: {'x', 'y', 'f(x,y)'} 3: ε 2: (∆x)next 1: CURRENT Thus, this function is used to determine the appropriate size of a time step ((∆x)next) to satisfy the required tolerance, and the method used to arrive at that result (CURRENT). The following screen shots show the RPN stack before and after application of function RRKSTEP: These results indicate that (∆x)next = 0.00558... and that the RKF method (CURRENT = 1) should be used. Page 16-73