Reference Guide
3-204 Full Command and Function Reference
•
error displays the absolute error for that step. A zero error indicates that the Runge–Kutta–
Fehlberg method failed and that Euler’s method was used instead.
The absolute error is the absolute value of the estimated error for a scalar problem, and the row
(infinity) norm of the estimated error vector for a vector problem. (The latter is a bound on the
maximum error of any component of the solution.)
Access: …µ
RKFE
Input/Output:
L
2
/A
1
L
1
/A
2
L
4
/I
1
L
3
/I
2
L
2
/I
3
L
1
/I
4
{ list }
h
→
{ list }
h
y
delta
error
L = Level; A = Argument; I = item
See also: RKF, RKFSTEP, RRK, RRKSTEP, RSBERR
RKFSTEP
Type: Command
Description: Next Solution Step for RKF Command: Computes the next solution step (h
next
) to an initial value
problem for a differential equation.
The arguments and results are as follows:
•
{ list } contains three items in this order: the independent (t) and solution (y) variables, and the
right-hand side of the differential equation (or a variable where the expression is stored).
•
x
tol
sets the tolerance value.
•
h specifies the initial candidate step.
•
h
next
is the next candidate step.
The independent and solution variables must have values stored in them. RKFSTEP steps these
variables to the next point upon completion.
Note that the actual step used by RKFSTEP will be less than the input value h if the global error
tolerance is not satisfied by that value. If a stringent global error tolerance forces RKFSTEP to
reduce its stepsize to the point that the Runge–Kutta–Fehlberg methods fails, then RKFSTEP
will use the Euler method to compute the next solution step and will consider the error tolerance
satisfied. The Runge-Kutta-Fehlberg method will fail if the current independent variable is zero
and the stepsize ≤ 1.3 × 10
-498
or if the variable is nonzero and the stepsize is 1.3 × 10
-10
times its
magnitude.
Access: …µ
RKFS
Input/Output:
L
3
/A
1
L
2
/A
n
L
1
/A
n+1
L
3
/I
1
L
2
/I
2
L
1
/I
3
{ list }
x
tol
h
→
{ list }
x
tol
h
next
L = Level; A = Argument; I = item
See also: RKF, RKFERR, RRK, RRKSTEP, RSBERR
RL
Type: Command
Description: Rotate Left Command: Rotates a binary integer one bit to the left.
The leftmost bit of #n
1
becomes the rightmost bit of #n
2
.
Access: … ã
BIT RL
(ã is the right-shift of the 3key).
Flags: Binary Integer Wordsize (–5 through –10), Binary Integer Base (–11, –12)