Re: OT: Looking for a good physics site
 

Sorry, I cut/pasted from a post I did in another web site; the attitude probably comes from some hostility experienced there.

Re: OT: Looking for a good physics site
 

No problem.

Hey, if that thread has the solution, could you point me to it?

Re: OT: Looking for a good physics site
 

By 'distance' I meant we didn't take into account position. That wasn't worded well.

Yes we did; the very definition of intercepting a target object is when the positions are equal. We have two position equations, with two unknowns (time and position). Since we know the positions must be equal, we can simply substitute one of the equations for the S value (position) in the other equation, thus eliminating it.

So I should make two formulas, one with a '+' there and the other with a '-' there and if one returns a zero, I use the other?

No... both will return zeros of the quadratic function (aka x-intercepts). I wasn't talking about the integer value 0. A negative zero/intercept is thrown out, as per previous post.

Re: OT: Looking for a good physics site
 

...I'm missing something here. You're saying the positions must be equal, but at the same time they start unequal.

No... both will return zeros of the quadratic function (aka x-intercepts). I wasn't talking about the integer value 0. A negative zero/intercept is thrown out, as per previous post.
...I have no idea what you just said. I can't even decypher the grammer. For one thing, the only zero I've ever known is an integer, except for the fact that zero isn't actually all that numerical.

Re: OT: Looking for a good physics site
 

...I'm missing something here. You're saying the positions must be equal, but at the same time they start unequal.

Huh? Unknown and unequal are not the same thing.

...I have no idea what you just said.

http://en.wikipedia.org/wiki/Zero_of_a_function

Re: OT: Looking for a good physics site
 

I'm missing something. Probably something obvious. Are you saying the function backtracks from where the positions are equal to where they are at start?

Ok, so occasionally the formula will return zero.

Perhaps it would help if you looked at my code? It could help us figure out the difference between what I think I should be doing versus what I should actually be doing.

Re: OT: Looking for a good physics site
 

The two final positions are variables, and unknown. But they are equal to each other by definition, since equal positions is the definition of interception.
Knowing that they are both equal reduces the number of unknowns by one (Instead of positionA and positionB, you have two copies of positionIntercept). This allows you to solve for Time. If the interception is impossible, Time will end up being an imaginary number.

Re: OT: Looking for a good physics site
 

Ok, thanks, that makes sense.

One of the problems is that it tends to flicker between thinking it is unsolveable and having an intercept angle. (I have a bit of code that gives it an angle of '0' if it's unsolveable). That's one reason I posted the code.

You guys are great, you know that, right?

Re: OT: Looking for a good physics site
 

Ok, so occasionally the formula will return zero.

If one of the zeros/x-intercepts of the equation occurs at 0,0, then sure... The formula always returns two zeros/x-intercepts; that is the entire purpose of it.

Re: OT: Looking for a good physics site
 

Oh, you mean it returns an intercept that is zero relative to the target.

Ok, so it should work. Now I just have to figure out why my implementation doesn't.