Hi
I’m a newbie to Mathematica (having played with it for just three days), so apologies for what might seem a dumb question. I can’t find anywhere (even in the Help) a function for calculating the digital sum and the digital root of an integer. I can do it programmatically, but surely there is a built-in function or command for these common digit-manipulation tasks.
Cheers
Geoffrey Marnell
One way to implement these would be
digitalSum[k_Integer] := Total@IntegerDigits[k]
digitalRoot[k_Integer] := FixedPoint[digitalSum, k]
FixedPoint will repeatedly apply digitalSum until the result does not change. A more explicit implementation could use NestWhile, with a check on the number of digits. But this trick with FixedPoint makes the code shorter.
Or for the digital root you could use
digitalroot[k_Integer] := Mod[k - 1, 9] + 1
Mod accepts a third argument, making this easier:
digitalroot[k_Integer] := Mod[k, 9, 1]
Thank you Szabolcs, Paul and Sander. This all works perfectly. I am intrigued by “offset”. The accompanying documentation doesn’t explain how it affects mod calculations. It works, but it puzzles me.
Cheers
Geoffrey
Thanks Sander. Silly me. I searched the help for “Offset” and got nothing of relevance Clearly, I should have searched for Mod!!
Cheers
Geoffrey
