User Guide

Page 16-74
Function RKFERR
This function returns the absolute error estimate for a given step when solving
a problem as that described for function RKF. The input stack looks as
follows:
2: {‘x’, ‘y’, ‘f(x,y)’}
1: ∆x
After running this function, the stack will show the lines:
4: {‘x’, ‘y’, ‘f(x,y)’}
3: ε
2: ∆y
1: error
Thus, this function is used to determine the increment in the solution, ∆y, as
well as the absolute error (error).
The following screen shots show the RPN stack before and after application of
function RKFERR:
These result show that ∆y = 0.827… and error = -1.89…×10
-6
.
Function RSBERR
This function performs similarly to RKERR but with the input elements listed for
function RRK. Thus, the input stack for this function will look as follows:
2: {‘x’, ‘y’, ‘f(x,y)’ ‘∂f/∂x’ ‘∂f/vy’ }
1: ∆x
After running the function, the stack will show the lines:
4: {‘x’, ‘y’, ‘f(x,y)’ ‘∂f/∂x’ ‘∂f/vy’ }:
3: ε
2: ∆y
1: error