Recursion?

[cubsfan334]

Hi, I have one more question: How would I make a recursive function? For example I could have these equations:

a1 = (x1 - x2) * t
a2 = (y1 - y2) * t

x1f = 5 * a1
y1f = 5 * a2

I need a do loop that will calculate x1f and y1f when t=1, then plug in the previously generated xf1 for x1 and yf1 for y1 when t=2, etc, and keep doing that.

How would I program this?

Thanks,
cubsfan

 

[xwb]

Not all versions of Fortran will do recursion but you don't need recursion to do what you require

! Reverse what will happen
x1f = x1
y1f = y1
do t = 1, n, 1
   ! Take the old values
   x1 = x1f
   y1 = y1f
   a1 = (x1 - x2) * t
   a2 = (y1 - y2) * t

   x1f = 5 * a1
   y1f = 5 * a2
end do

You can optimize this a bit by reusing x1, y1 and not bothering with x1f,y1f

do t = 1, n, 1
   a1 = (x1 - x2) * t
   a2 = (y1 - y2) * t

   x1 = 5 * a1
   y1 = 5 * a2
end do

You could even dispense with a1 and a2

do t = 1, n, 1
   x1 = 5 * (x1 - x2) * t
   y1 = 5 * (y1 - y2) * t
end do

 

[cubsfan334]

I'm not sure about the first code you posted, but I don't think the 2nd and 3rd will work. I think those simply plug n in for t and solve. What I need is the result for t=2 is dependent on the result of t=1, and the result of t=3 depends on the result of t=2, etc

If that makes sense.

 

[xwb]

Try a dry run with figures - you'll find that all 3 give the same result according to your spec. Alternatively, just print x1, y1, t.

Do x2, y2 always remain the same?