Home |
Search |
Today's Posts |
#1
Posted to microsoft.public.excel.programming
|
|||
|
|||
Variable Step rates in loops
I am working on an astronomy project where I need to get all the
conjunctions of 2 planets between 2 dates. I have functions that give me the Longitude of each planet and the Angular Separation between 2 longitudes. These are based on a Julian Day. I need help with how to get the most accurate date/time of each event where PAS (Planetry Angular Separation) = 0 or less than X (say 0.001*) When I step thur my routine with the Julian Day (JD) by 1 I dont get the precision as if I steped thru at 0.0001. Obvously the 0.0001 step would take forever if I am searching over 30 years. Is there a way to have a variable STEP that reduces based on the value of my PAS? Then once one event is solved, the step would go back to 1 and start the loop over? Thanks |
#2
Posted to microsoft.public.excel.programming
|
|||
|
|||
Variable Step rates in loops
gtslabs;230211 Wrote: I am working on an astronomy project where I need to get all the conjunctions of 2 planets between 2 dates. I have functions that give me the Longitude of each planet and the Angular Separation between 2 longitudes. These are based on a Julian Day. I need help with how to get the most accurate date/time of each event where PAS (Planetry Angular Separation) = 0 or less than X (say 0.001*) When I step thur my routine with the Julian Day (JD) by 1 I dont get the precision as if I steped thru at 0.0001. Obvously the 0.0001 step would take forever if I am searching over 30 years. Is there a way to have a variable STEP that reduces based on the value of my PAS? Then once one event is solved, the step would go back to 1 and start the loop over? Thanks Hello gtslabs, I am not an astronomer, so I can't fully answer your question. What you need is a recursive VBA Function. The function would need to be seeded and then the results of the algorithm are fed back into the function as arguments. There needs to be some check inside the algorithm to determine when the function should stop calculating and return the result. Which algorithm or algorithms you need I can't say. If I owned a copy of Jean Meeus book "Astronomical Algorithms, second edition", I probably could. Perhaps someone who is an astronomer will be able to offer you more insight. I do know that it is possible. -- Leith Ross Sincerely, Leith Ross 'The Code Cage' (http://www.thecodecage.com/) ------------------------------------------------------------------------ Leith Ross's Profile: http://www.thecodecage.com/forumz/member.php?userid=75 View this thread: http://www.thecodecage.com/forumz/sh...ad.php?t=64330 |
#3
Posted to microsoft.public.excel.programming
|
|||
|
|||
Variable Step rates in loops
Hi. Would a simple linear interpolation function work for you?
If at day 10, planet a is 4 degrees ahead of B, and on day 20 it is -12 degrees behind, then a very simple next guess might be... Sub Example() Debug.Print NextGuess(10, 4, 20, -12) End Sub Returns: 12.5 Meaning that a guess of when they were the closest is day 12, at around noon. Use this, and the closest of the previous two observations, and loop again. Function NextGuess(t1, d1, t2, d2) 'Time 1, Difference 1, time 2, Difference 2 NextGuess = (d1 * t2 - d2 * t1) / (d1 - d2) End Function = = = HTH :) Dana DeLouis gtslabs wrote: I am working on an astronomy project where I need to get all the conjunctions of 2 planets between 2 dates. I have functions that give me the Longitude of each planet and the Angular Separation between 2 longitudes. These are based on a Julian Day. I need help with how to get the most accurate date/time of each event where PAS (Planetry Angular Separation) = 0 or less than X (say 0.001*) When I step thur my routine with the Julian Day (JD) by 1 I dont get the precision as if I steped thru at 0.0001. Obvously the 0.0001 step would take forever if I am searching over 30 years. Is there a way to have a variable STEP that reduces based on the value of my PAS? Then once one event is solved, the step would go back to 1 and start the loop over? Thanks |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Loan amortization schedule for variable interest rates | Excel Worksheet Functions | |||
Can Step through but when run defines variable wrong | Excel Programming | |||
How show value of variable in single step debug mode? | Excel Programming | |||
Loops or Do/ while or STEP !!!! A better solution | Excel Programming | |||
variable string and loops | Excel Programming |