Tell Wolfram Alpha that a variable is a natural number

Question

How can I tell Wolfram Alpha that some variables are natural numbers, when I want to solve a equation?

An example of what I want to do:

$\binom{n}{k}\cdot p^k \cdot (1-p)^{n-k} = \frac{1}{\sqrt{n\cdot p \cdot (1-p)}}\cdot \frac{1}{\sqrt{2 \cdot \pi}} \cdot e^{-\frac{1}{2} \cdot \left(\frac{x-np}{\sqrt{n \cdot p \cdot (1-p)}}\right)^2}$ solve for $x$ with $n,k \in \mathbb{N}$, $0 \lt p \lt 1$.

i have the same problem, here's an example @Amzoti : sum_{i=1}^{infinity}(1/2)^i*(1-p)^(i-1) assuming p in ]0,1[ — philx_x, Apr 26 '17 at 09:04
This works in wolfram alpha (tested now): > solve (x-3/2)(x-2)=0 over the naturals — Ruben, Apr 16 '21 at 16:17

score 8 · Answer 1 · answered Oct 31 '13 at 17:03

8

Just add an "assuming x integer" at the end. I tested it, and it seems to work. (similar to Maple's notation assuming x::integer, I guess) For natural it doesn't seem to work properly: assuming x natural

answered Oct 31 '13 at 17:03

AlexR

25,110

14

This doesn't seem to work anymore. – Skeen Oct 10 '17 at 18:38
@Skeen Pardon me, but my link seems to work. Funny enough, even assuming x natural works (just click the link) – AlexR Oct 10 '17 at 21:20
2

I'm getting this: Wolfram|Alpha does not yet know how to respond to your exact query. The "closest interpretation" is based on lexical and semantic similarity in Wolfram|Alpha's computable knowledge space. – Skeen Oct 11 '17 at 15:03
Can you give a link? As I said, I have no problem with the link in my Answer - it simplifies Gamma(x) to (x+1)! using the assumption that x is an integer. – AlexR Oct 11 '17 at 16:08

mathematics2x2life · Answer 2 · 2019-08-15T15:26:12.900

4

It depends on how you are trying what it is you are trying to solve. Telling Mathematica that something is an integer has a different syntax depending on what you are trying to do.

Assuming that you are using the "Solve" function, it would look like this:

Solve[(x - 3/2) (x - 2)== 0 && x \[Element] Integers]

EDIT. After 6 years, the website has changed and this no longer works. However,

 Solve (x-3/2)(x-2)=0 for x integer

seemed to work, as you can can see here.

edited Aug 15 '19 at 15:26

answered Oct 31 '13 at 17:05

mathematics2x2life

13,578

This does not work for wolfram alpha. – Krupip Aug 15 '19 at 14:54
@opa Thank you. After 6 years, the site has changed a lot. – mathematics2x2life Aug 15 '19 at 15:25
And how would we specify that all variables in the expression are real? Thank you – Confounded Nov 12 '21 at 09:29

score 3 · Answer 3 · answered Mar 09 '19 at 15:16

3

As dirty as this is, I've used modulus 1 to force numbers to be integers. Combine with a >= 0 restriction and you can reach Natural numbers.

Example

answered Mar 09 '19 at 15:16

BlackVegetable

191
1
8

score 0 · Answer 4 · answered Nov 13 '15 at 17:51

0

Solve[ ..., Element[..., Integers]]

answered Nov 13 '15 at 17:51

laborator

19

3

This does not work for wolfram alpha – Krupip Aug 15 '19 at 14:54

Tell Wolfram Alpha that a variable is a natural number

4 Answers4

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