# Modulo ?

Discussion in 'Ruby' started by Zayd Connor, Mar 19, 2009.

1. ### Zayd ConnorGuest

Zayd Connor, Mar 19, 2009

2. ### 7stud --Guest

Zayd Connor wrote:
> Maybe i need to get some sleep, but can someone explain how modulos
> work?
>
> Thanks

result = 7 % 3
puts result

--output:--
1

7 has two 3's in it, and after removing those two 3's from 7, the
remainder is 1.

--
Posted via http://www.ruby-forum.com/.

7stud --, Mar 19, 2009

3. ### Brian AdkinsGuest

Zayd Connor <> writes:

> Maybe i need to get some sleep, but can someone explain how modulos
> work?

From "Discrete Mathematics by Rosen":

"Let a be an integer and m be a positive integer. We denote by a mod m
the remainder when a is divided by m.

It follows from the definition of remainder that a mod m is the
integer r such that:

a = q * m + r and 0 <= r < m "

This is all assuming you didn't type an 'o' when you meant 'e'

--
http://lojic.com/

Brian Adkins, Mar 19, 2009
4. ### Robert KlemmeGuest

On 19.03.2009 06:50, Zayd Connor wrote:
> Maybe i need to get some sleep, but can someone explain how modulos
> work?

http://lmgtfy.com/?q=modulo

Robert Klemme, Mar 19, 2009
5. ### Rob BiedenharnGuest

On Mar 19, 2009, at 10:22 AM, Robert Klemme wrote:

> On 19.03.2009 06:50, Zayd Connor wrote:
>> Maybe i need to get some sleep, but can someone explain how modulos
>> work?

>
> http://lmgtfy.com/?q=modulo
>

This seems completely unnecessary. There was already a great response
from Brian who not only directly addressed the "modulos", but also
picked up and pointed out (subtly) that the question might have been
about "modules". Something that makes perfect sense, but I certainly
didn't see that possibility.

And did you Google modulo or module yourself to see how useful the
result really is? If you're going to simply shout lmgtfy, at least put
"ruby" in there, too (well, for module, not for modulo ;-)

-Rob

Rob Biedenharn http://agileconsultingllc.com

Rob Biedenharn, Mar 19, 2009
6. ### Robert KlemmeGuest

On 19.03.2009 15:40, Rob Biedenharn wrote:
> And did you Google modulo or module yourself to see how useful the
> result really is?

I did.

robert

Robert Klemme, Mar 19, 2009
7. ### Zayd ConnorGuest

Rob Biedenharn wrote:
> On Mar 19, 2009, at 10:22 AM, Robert Klemme wrote:
>
>> On 19.03.2009 06:50, Zayd Connor wrote:
>>> Maybe i need to get some sleep, but can someone explain how modulos
>>> work?

>>
>> http://lmgtfy.com/?q=modulo
>>

>
>
> This seems completely unnecessary. There was already a great response
> from Brian who not only directly addressed the "modulos", but also
> picked up and pointed out (subtly) that the question might have been
> about "modules". Something that makes perfect sense, but I certainly
> didn't see that possibility.
>
> And did you Google modulo or module yourself to see how useful the
> result really is? If you're going to simply shout lmgtfy, at least put
> "ruby" in there, too (well, for module, not for modulo ;-)
>
> -Rob
>
> Rob Biedenharn http://agileconsultingllc.com
>

Thanks guys,(singing) I can see clearly now the rain is gone . Maybe I
should have been more clear and added the % sign when mentioning modulo,
so I wouldn't confuse anyone thinking I meant modules

Thanks

--
Posted via http://www.ruby-forum.com/.

Zayd Connor, Mar 19, 2009
8. ### Michael MaloneGuest

> Thanks guys,(singing) I can see clearly now the rain is gone . Maybe I
> should have been more clear and added the % sign when mentioning modulo,
> so I wouldn't confuse anyone thinking I meant modules
>
> Thanks
>
>

Though there is one thing I would like to point out: 0 % 7 = 0
So 'remainder' is not strictly true

Michael

=======================================================================
This email, including any attachments, is only for the intended
addressee. It is subject to copyright, is confidential and may be
the subject of legal or other privilege, none of which is waived or
lost by reason of this transmission.
If the receiver is not the intended addressee, please accept our
apologies, notify us by return, delete all copies and perform no
other act on the email.
Unfortunately, we cannot warrant that the email has not been
altered or corrupted during transmission.
=======================================================================

Michael Malone, Mar 19, 2009
9. ### Sebastian HungereckerGuest

Michael Malone wrote:
> Though there is one thing I would like to point out: 0 % 7 = 0
> So 'remainder' is not strictly true

Sorry I don't follow you. What's the remainder of 0/7 if not 0?
0-7*0 is 0, is it not?

Confused,
Sebastian

Sebastian Hungerecker, Mar 19, 2009
10. ### Michael MaloneGuest

Sebastian Hungerecker wrote:
> Michael Malone wrote:
>
>> Though there is one thing I would like to point out: 0 % 7 = 0
>> So 'remainder' is not strictly true
>>

>
> Sorry I don't follow you. What's the remainder of 0/7 if not 0?
> 0-7*0 is 0, is it not?
>
> Confused,
> Sebastian
>
>

Many people I know and work with simplify the modulo operator to
themselves as remainder, so mentally (whether or not it is correct)
assume 0/7 = 0 r 7
I am just making an explicit example of this not necessarily obvious
case. It's totally fine when one knows the semantics of modulo, it's
the simplification to remainder that many people make that causes
problems here.

Michael

=======================================================================
This email, including any attachments, is only for the intended
addressee. It is subject to copyright, is confidential and may be
the subject of legal or other privilege, none of which is waived or
lost by reason of this transmission.
If the receiver is not the intended addressee, please accept our
apologies, notify us by return, delete all copies and perform no
other act on the email.
Unfortunately, we cannot warrant that the email has not been
altered or corrupted during transmission.
=======================================================================

Michael Malone, Mar 19, 2009
11. ### Rob BiedenharnGuest

On Mar 19, 2009, at 5:07 PM, Michael Malone wrote:

> Sebastian Hungerecker wrote:
>> Michael Malone wrote:
>>
>>> Though there is one thing I would like to point out: 0 % 7 = 0
>>> So 'remainder' is not strictly true
>>>

>>
>> Sorry I don't follow you. What's the remainder of 0/7 if not 0?
>> 0-7*0 is 0, is it not?
>>
>> Confused,
>> Sebastian
>>
>>

> Many people I know and work with simplify the modulo operator to
> themselves as remainder, so mentally (whether or not it is correct)
> assume 0/7 = 0 r 7
> I am just making an explicit example of this not necessarily obvious
> case. It's totally fine when one knows the semantics of modulo,
> it's the simplification to remainder that many people make that
> causes problems here.
>
> Michael

[I hope this survives email formatting...]

__0_r_0_
7 ) 0
0*7 => -0
==
0

Just because people can't understand division and remainders isn't
enough to keep them away from technical discussions. The original
response (which I deleted months ago [or was that yesterday?]) had an
accurate definition.

-Rob

Rob Biedenharn http://agileconsultingllc.com

Rob Biedenharn, Mar 19, 2009
12. ### Sebastian HungereckerGuest

Michael Malone wrote:
> Many people I know and work with simplify the modulo operator to
> themselves as remainder, so mentally (whether or not it is correct)
> assume 0/7 = 0 r 7

Maybe I'm slow, but I don't get it.
You're saying that many people assume that x % y is the same as the remainder
of dividing x by y, right? I don't see anything wrong with that.
If I understand you correctly, you're also saying that this assumption is
wrong in the case of 0%7. I don't understand why that should be the case. The
remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?

Still confused,
Sebastian

Sebastian Hungerecker, Mar 19, 2009
13. ### Michael MaloneGuest

Sebastian Hungerecker wrote:
> Michael Malone wrote:
>
>> Many people I know and work with simplify the modulo operator to
>> themselves as remainder, so mentally (whether or not it is correct)
>> assume 0/7 = 0 r 7
>>

>
> Maybe I'm slow, but I don't get it.
> You're saying that many people assume that x % y is the same as the remainder
> of dividing x by y, right? I don't see anything wrong with that.
> If I understand you correctly, you're also saying that this assumption is
> wrong in the case of 0%7. I don't understand why that should be the case. The
> remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?
>
> Still confused,
> Sebastian
>
>

Sorry for confusing everyone here, I just know of a particular case
where 0%7 = 7 was assumed. I was trying to stop this happening again,
but I think I've caused more confusion than it's worth. Sorry folks.
Ignore my post and you'll sleep more easily.

Michael

=======================================================================
This email, including any attachments, is only for the intended
addressee. It is subject to copyright, is confidential and may be
the subject of legal or other privilege, none of which is waived or
lost by reason of this transmission.
If the receiver is not the intended addressee, please accept our
apologies, notify us by return, delete all copies and perform no
other act on the email.
Unfortunately, we cannot warrant that the email has not been
altered or corrupted during transmission.
=======================================================================

Michael Malone, Mar 19, 2009
14. ### Brian AdkinsGuest

Robert Klemme <> writes:

> On 19.03.2009 06:50, Zayd Connor wrote:
>> Maybe i need to get some sleep, but can someone explain how modulos
>> work?

>
> http://lmgtfy.com/?q=modulo

That is *awesome* ! Sponsored by "Backpack" - interesting.

--
http://lojic.com/

Brian Adkins, Mar 19, 2009
15. ### John W KennedyGuest

On 3/19/09 6:03 PM, Sebastian Hungerecker wrote:
> Michael Malone wrote:
>> Many people I know and work with simplify the modulo operator to
>> themselves as remainder, so mentally (whether or not it is correct)
>> assume 0/7 = 0 r 7

>
> Maybe I'm slow, but I don't get it.
> You're saying that many people assume that x % y is the same as the remainder
> of dividing x by y, right? I don't see anything wrong with that.
> If I understand you correctly, you're also saying that this assumption is
> wrong in the case of 0%7. I don't understand why that should be the case. The
> remainder of 0/7 is 0, right? And 0%7 is also 0, so where's the problem?

Going by the usual definition of "remainder", there is a difference
between modulo and remainder when negative numbers get involved.

remainder(a,b) = a - trunc(a/b) * b
modulo(a,b) = a - floor(a/b) * b

John W Kennedy, Mar 20, 2009
16. ### Yossef MendelssohnGuest

On Mar 19, 5:15=A0pm, Michael Malone <> wrote:
> Sorry for confusing everyone here, I just know of a particular case
> where 0%7 =3D 7 was assumed.

This is confusing. As in 0%7 =3D 7 is very confusing.

A mod B shouldn't have a result that's equal to or greater than B. If
that happens, you take a B out until you can't anymore. The remainder
when A is divided by B is the same thing. If you end up with something
greater than B, you stopped too soon.

As John W. Kennedy pointed out, the difference between modulo and a
simple remainder comes up when dealing with negative numbers.

--
-yossef

Yossef Mendelssohn, Mar 20, 2009