Is there any chance that this power series converges p-adically in the rational fieldin $mathbb{Q}$?
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Consider the p-adic power series $ sum _{n=1}^{infty} frac{x^n}{u^n}$. Consider the usual absolute value $|.|$ and p-adic absolute value $|.|_p$ on $ mathbb{Q}$, where $ u in mathbb{Q}$.
Is there any chance that this power series converges p-adically in the rational field $mathbb{Q}$ or $ sum frac{x^n}{u^n} in mathbb{Q} $ ?
We know that a power series $ sum a_n x^n$ converges p-adically iff $ |a_nx^n|_p to 0$.
Now for the given power series $ a_n=frac{1}{u^n}$ and $ |a_n|_p=|frac{1}{u^n}|_p to 0$ if $ p $ does not divide $ u$.
In the above case what would be the sum of the power series?
Can the sum be a rational number?
Help me
sequences-and-series p-adic-number-theory
$endgroup$
|
show 10 more comments
$begingroup$
Consider the p-adic power series $ sum _{n=1}^{infty} frac{x^n}{u^n}$. Consider the usual absolute value $|.|$ and p-adic absolute value $|.|_p$ on $ mathbb{Q}$, where $ u in mathbb{Q}$.
Is there any chance that this power series converges p-adically in the rational field $mathbb{Q}$ or $ sum frac{x^n}{u^n} in mathbb{Q} $ ?
We know that a power series $ sum a_n x^n$ converges p-adically iff $ |a_nx^n|_p to 0$.
Now for the given power series $ a_n=frac{1}{u^n}$ and $ |a_n|_p=|frac{1}{u^n}|_p to 0$ if $ p $ does not divide $ u$.
In the above case what would be the sum of the power series?
Can the sum be a rational number?
Help me
sequences-and-series p-adic-number-theory
$endgroup$
2
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
1
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
3
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
6
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
2
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46
|
show 10 more comments
$begingroup$
Consider the p-adic power series $ sum _{n=1}^{infty} frac{x^n}{u^n}$. Consider the usual absolute value $|.|$ and p-adic absolute value $|.|_p$ on $ mathbb{Q}$, where $ u in mathbb{Q}$.
Is there any chance that this power series converges p-adically in the rational field $mathbb{Q}$ or $ sum frac{x^n}{u^n} in mathbb{Q} $ ?
We know that a power series $ sum a_n x^n$ converges p-adically iff $ |a_nx^n|_p to 0$.
Now for the given power series $ a_n=frac{1}{u^n}$ and $ |a_n|_p=|frac{1}{u^n}|_p to 0$ if $ p $ does not divide $ u$.
In the above case what would be the sum of the power series?
Can the sum be a rational number?
Help me
sequences-and-series p-adic-number-theory
$endgroup$
Consider the p-adic power series $ sum _{n=1}^{infty} frac{x^n}{u^n}$. Consider the usual absolute value $|.|$ and p-adic absolute value $|.|_p$ on $ mathbb{Q}$, where $ u in mathbb{Q}$.
Is there any chance that this power series converges p-adically in the rational field $mathbb{Q}$ or $ sum frac{x^n}{u^n} in mathbb{Q} $ ?
We know that a power series $ sum a_n x^n$ converges p-adically iff $ |a_nx^n|_p to 0$.
Now for the given power series $ a_n=frac{1}{u^n}$ and $ |a_n|_p=|frac{1}{u^n}|_p to 0$ if $ p $ does not divide $ u$.
In the above case what would be the sum of the power series?
Can the sum be a rational number?
Help me
sequences-and-series p-adic-number-theory
sequences-and-series p-adic-number-theory
edited Dec 28 '18 at 11:46
arifamath
asked Dec 28 '18 at 11:02
arifamatharifamath
1196
1196
2
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
1
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
3
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
6
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
2
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46
|
show 10 more comments
2
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
1
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
3
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
6
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
2
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46
2
2
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
1
1
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
3
3
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
6
6
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
2
2
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46
|
show 10 more comments
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2
$begingroup$
The OP surely means to ask whether the $p$-adic limit lies in $mathbb Q subseteq mathbb Q_p$?
$endgroup$
– Layer Cake
Dec 28 '18 at 11:28
1
$begingroup$
@LayerCake, Yes I mean that p-adic limit lies in $mathbb{Q}$
$endgroup$
– M. A. SARKAR
Dec 28 '18 at 11:32
3
$begingroup$
This obviously depends on $x,u$. For $x=p,u=1$ the series converges to $-1/(p-1)$
$endgroup$
– Wojowu
Dec 28 '18 at 11:35
6
$begingroup$
We are looking at a geometric series, which converges in $mathbb Q_p$ iff $|frac{x}{u}|_p<1$. The limit then is $1/(1-x/u)-1$ and whether it lies in $mathbb Q$ depends on $x$.
$endgroup$
– Layer Cake
Dec 28 '18 at 11:39
2
$begingroup$
Quite generally, the limit of a convergent geometric series $sum _{n=0}^{infty}q^n$ is $1/(1-q)$. You can prove this by looking at the n-th partial sum and then taking the limit (bearing in mind that $ q^n to 0$).
$endgroup$
– Layer Cake
Dec 28 '18 at 11:46