Thread: dogs chasing cats up trees

Originally Posted by nonoob

Strategy might be as simple as:
Calculate distance from initial cat position to all the trees. Find closest one. Is it 2x distance from dog to cat?

But while the cat is heading off to any particular tree, should the dog aim for the same tree? Or aim for the cat at its anticipated position of intercept dynamically? Or travel in some curve? Now the problem starts to get all differential equationy. What if cat heads for tree #1, then takes a quick turn and goes for tree #2? Dog has to alter his path. I think this is too hard to solve.

I tend to agree... this isn't the kind of problem you would hand someone in an introductory C class. It is solvable, of course, but probably not within the confines of small programs expected by most instructors and certainly not within a week...

Reading these threads I do find myself wondering what the heck these so called "professors" are trying to accompish...

That's the trouble of being out of school so long and getting jaded by the real world... you tend to see everything complicated (real world). But I doubt the problem was meant to be as difficult.

Instead of calculating distance to all trees, why not just find the first tree (in any order) whose distance from cat is 2x distance cat-to-dog. Stop there, the problem is solved.

You mean less than 2X distance of cat to dog, of course.

Sure, cat is sitting pretty in the treetops.

Ok. Thinking more about it... the problem is actually complicated.
Dog = "D", tree = "T", cat = "C"
The above method only works if dog, tree, cat are co-linear.

D ***** T ********** C
---> <---
Dog and cat head for the tree (towards each other). Cat can do twice the speed, so it starts at 2x the distance from the tree. Great. That's the equilibrium point.

Now what if dog, cat, tree are at some other angle with respect to each other.

When dog covers a certain distance towards cat, cat has also moved. When does dog catch up?

The dog doesn't care about any tree's, because it spotted the cat -- it is only interested in getting to the cat, and will take the shortest path to get there. It will not "head for the tree to cut off the cat", or any such strategy. For all intents and purposes, it's a straight line. Dogs in the heat of a chase, don't do any math. They will cut a corner in their pursuit, if possible, but there are no obstacles or mitigating factors in the environment, mentioned, here. Just dog, cat, trees, and distances

The cat is always going to run, in as straight a line as possible, to the nearest tree. Anything more is beyond the scope of this problem, imo.

The cat won't head in an oblique angle to the dog. They would be extinct if they made that a habit, since the dog would angle straight toward the cat then, vastly shortening the distance between them.

Yes, a cat will "spring" into any immediately available tree, in any direction as the dog approaches, but this problem tells us it's a chase, so the cat will be running directly away from the dog, and the dog will be directly following. If some obstacles were mentioned, or the cat and dog had just spied each other, then EVERYTHING would change. For this problem, the cat is out in a barren environment, with just the trees to use for safety, and no angling by dog or cat, need to be considered.

Yes the cat would head off in an oblique direction if a tree in that vector is closest. A cat might even head TOWARDS the dog if a tree is in line and close. Although instinctively it may not want to do that.

I think we need to plot a locus of points where cat & dog intersect. Probably some form of ellipsoid or conchoid. Then we see if there are any tree coordinates within that area.

Code:

 
int main()
      {
       
      FILE *fp;
       
   if((fp = fopen("CatAndDog.dat","r")) == NULL)
   printf("File could not be opened\n")

  fscanf(fp, "%d %d", &a, &b);
  fscanf(fp, "%d %d", &c, &d);
  fscanf(fp, "%d", &e);
  }

the a,b,c,d,e are the coordinators of the cat, dog and trees. i also have done a loop to read all the coodrinators of the trees. What i don't know how to do is how to check if the cat can escape or not and also how to pick the closest tree to the cat if there are two or more.

Originally Posted by nonoob

Yes the cat would head off in an oblique direction if a tree in that vector is closest. A cat might even head TOWARDS the dog if a tree is in line and close. Although instinctively it may not want to do that.

I think we need to plot a locus of points where cat & dog intersect. Probably some form of ellipsoid or conchoid. Then we see if there are any tree coordinates within that area.

So you're taking a relatively simple programming problem, smack into the next realm, eh?

Shades of Clinton, it all boils down to what your definition of "chasing" is.

Sadam, despite being given advice on multiple forums, you've done nothing substantive, so far. Re-read itsme86's post, and get onto doing that - at least try. Just opening a file and reading in the values, does NOT show much.

can anyone solve it?

Originally Posted by Mario F.

You suggested an array of a Point structs, Adak suggested a matrix representing the map. What's the problem? It's a kindergarten exercise. Not a spacecraft prototype.

Really? Kindergarten... So you should be able to manage a solution very nicely then...

So lets see it... where is your solution?