Beginner question again.I quick task I set myself was to write ONE ITERATION of
the Collatz function for a given positive
integer.http://en.wikipedia.org/wiki/Collatz_conjecture
So my verb is supposed to do 3*n+1 if n is odd and n/2 if n is even.In a more
imperative/OOE based language (C/C++/Java) I could write this in less than a
minute. Unfortunately, I fell at the very first hurdle in J.
I originally wrote my tacit verb for even ints:collatz_even =.2&(%~)
collatz_even 4
2
This works, but I had a terrible time trying to put the brackets in the right
place. I am not sure why %~ needs to be bracketed. Won't J parse %~ as dyadic
and "know" that the left operand is 2?
Next I tried to do the case for odd n:
collatz_odd =. 1&+@(3&*) collatz_odd 3
10
That seems to work ok.Now I am not sure how to do an if statement in J. In
plain English I want "If n is even do collatz_even else do collatz_odd".The
verb I wrote to test for even-ness is
ones =. {:@#: NB. Finds the ones column values. 1 => odd, 0=> even
1 = ones 2
0
So I have a test but I am not sure how to utilize this test. How should I go
about doing:"If n is even do collatz_even else do collatz_odd"?
Thanks and regards,Jon
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