在Python中穿越海拔

Question

I am trying to run a Python script that calculates the trajectory of an object from the ground up above 100,000-meters then back below 100,000-meters. I want to be able to figure out how much time is spent above 100,000-meters. I have my trajectory code just fine (Runge-Kutta), and I can get up to 100,000-meters. However, I cannot figure out the right Python algorithm to keep going up to max altitude and start coming down to below 100,000-meters.

Here is what I have:

while (states[4,(i - 1)] >= 100000 and states[4,i] <= 100000 or states[4,i] != 100000):

I'm ending up in an infinite loop, though. states[4,i] is the altitude. My thinking is that if the previous ( i - 1 ) altitude is above 100,000-meters and the current ( i ) altitude is below 100,000-meters, I want it to exit the while loop. states[4,i] != 100000 is meant to get me up to that altitude, at least.

Thoughts?

Answer 1

I believe the issue you have here is that you need to keep track of when you cross the altitude. Why not just have a variable set to false before your loop, then true when you hit >= 100000, and add that to your while. Also, those conditionals are for leaving your loop, so you should negate it. Eg

reachedHeight = False
while (not (reachedHeight and states[4,(i - 1)] >= 100000 and states[4,i] <= 100000)):
  if (not reachedHeight and states[4,i] >= 100000):
    reachedHeight = True
  ...

Could also be a conditional with a break inside your loop.

Answer 2

The while loop you have above will continue looping unless states[4,i] equals 100,000.

False and False or True == True

This is likely why you are experiencing the infinite loop. You may want to remove the third case and if necessary, perform other checks inside the loop.