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Re: [Phys-L] Help w/ Euler Cromer algo.



Hi Bernard

This might help.

https://www.siue.edu/~mnorton/mat-340.pdf

Cheers

Fletch


Quoting Bernard Cleyet <bernard@cleyet.org>:

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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