Hello,
I’m new so haven’t done a lot of research on this site yet. So, I have dx/dt=f1(t,x,z), dy/dt=f2(t,y,z) where dx/dt and dy/dt have been coupled as shown by use of a third equation dz/dt=Adx/dt+Bdy/dt. My problem is that LibreOfficeCalc won’t do the math correctly in solving, simultaneously I guess, for x(t) and y(t) values due to incorrect Runge-Kutta coefficients K1,K2,K3,K4 (for x(t)) and L1,L2,L3,L4 (for y(t)). I have not ‘drag-copied’ the formulas for the individual time step rows, and am using absolute cell references in all formulas rather than range names. I have once obtained a graph with the exact shape of x(t) vs t, but the amplitude of x(t) doesn’t even get above 0.00 (to two decimals). Using a …mart HP laptop with Windows 11 OS. Should I expect success?? It also does fail as follows: When it computes the following non-RK constants in three cells as: 140,940,000 in cell T49, 563,760,000 in cell U49, and 281,880,000 in cell V49 and I then formulate in cell W49 the formula T49*U49-V49^2, W49 then shows 33,840, whereas my calculator says W49 should = 0.000. I guess I see the reason for the existence of programs like Matlab, which I don’t possess. Any advice??? Thanks
Please attach the spreadsheet, so we can see the actual formulas. In case the spreadsheet is large, reduce it as much as possible.
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OK. I misquoted the number above. I should have said "W49 then shows 67648, whereas......"
TDS BugAvoid ReDo RK4 Support.ods (72.0 KB)
And column labeled “c29” should rather be labeled as the variable “y(t)”.