ifactors Test Problem

09062017, 02:18 PM
Post: #1




ifactors Test Problem
I'm trying to create an is_prime function:
Code: EXPORT is_prime(X) dim(ifactors(7)) returns {2} but when I call is_prime(7), I get Error: Bad argument type. I tried with both upper and lowercase X and I tried the 2 both in and out of braces. What am I doing wrong? Tom L People may say I'm inept but I consider myself to be totally ept. 

09062017, 05:16 PM
(This post was last modified: 09062017 07:32 PM by Helge Gabert.)
Post: #2




RE: ifactors Test Problem
Try storing DIM(ifactors(X)) into a list, say L1, and then try
IF L1(1) == 2 THEN . . . Works here. (This is because, in Home, a statement like {2}=={2} returns {1}, not 1). But aside from that, why do you test DIM(ifactors(X))? That won't tell you if X is prime. 

09062017, 07:03 PM
(This post was last modified: 09062017 07:09 PM by toml_12953.)
Post: #3




RE: ifactors Test Problem
(09062017 05:16 PM)Helge Gabert Wrote: Try storing DIM(ifactors(X)) into a list, say L1, and then try I thought that if the length of the ifactors vector returns 2 then there are only two factors, the number itself and 1. I was wrong. The list doesn't include 1 so dim(ifactors(8)) would return 2 as well. Tom L People may say I'm inept but I consider myself to be totally ept. 

09062017, 07:10 PM
Post: #4




RE: ifactors Test Problem
(09062017 07:03 PM)toml_12953 Wrote: If the length of the ifactors vector returns 2 then there are only two factors, the number itself and 1. That means it's prime. Are you doing this as a learning exercise? (I'll leave alone the issue with this method to figure prime for someone else) The is already a function specifically for primes. Quite many in fact under the toolbox>CAS>Integer>Prime menu. TW Although I work for the HP calculator group, the views and opinions I post here are my own. 

09062017, 07:10 PM
Post: #5




RE: ifactors Test Problem
(09062017 05:16 PM)Helge Gabert Wrote: Try storing DIM(ifactors(X)) into a list, say L1, and then try You can also use EQ to compare two lists : IF EQ(DIM(ifactors(X)),{2}) THEN.... ...but ifactors(8) returns [2 3]: factor 2, multiplicity 3, so it won't help you to identify prime numbers. 

09062017, 08:13 PM
Post: #6




RE: ifactors Test Problem
Yeah, well, I'm not the OP and I never claimed that. Indeed,there are infinite cases of composite numbers which return {2} with this method.
I merely pointed out how to change the program to make it run, instead of coming up with the error message encountered by the OP. EQ()is a good suggestion, however. 

09062017, 10:12 PM
Post: #7




RE: ifactors Test Problem
(09062017 07:10 PM)Tim Wessman Wrote:(09062017 07:03 PM)toml_12953 Wrote: If the length of the ifactors vector returns 2 then there are only two factors, the number itself and 1. That means it's prime. Yes, I was just trying to come up with a function that didn't use the one from the menu. Thanks to all who answered my question! Tom L People may say I'm inept but I consider myself to be totally ept. 

09072017, 04:45 PM
Post: #8




RE: ifactors Test Problem
I forgot to mention:
You could use TYPE(ifactor(number to test)). For primes, should return 0. For composites, 8. (Of course, ifactor could return 0 for certain integers in error). 

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