Cromer claim the Last Point approximation is stable. So I must not
be writing it.
My use is (to begin with) a SHM oscillator:
SUB step
LET Q = -(g/L) * theta
LET thetadot = Q *deltat + thetadot
LET theta = theta + deltat * thetadot
LET t = t + deltat
END SUB
earlier:
OPTION ANGLE radians
For many of my “runs” I use g = 9.8 and L to make f (of 2Pi f) one second.
Just now using one ms deltat and fitting the result to a cos; the
first half second’s residuals are ~ 5e-9, doubling the second half
and by the third second (cycle) the maxima are 5 e-8 (radian).
Using a deltat of one tenth ms reduces the residuals only slightly!
What gives?
note: this would be acceptable if I didn’t need to run to 100 s and longer.
bc doesn’t want to necessarily use a fourth order approx.
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