Adapting the Chinese Remainder Theorem (CRT) for integers to polynomials Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)mod Distributive Law, factoring $!!bmod!!:$ $ abbmod ac = a(bbmod c)$Remainder of polynomial by product of 2 polynomials$f$ dividing by $x + 1$ have remainder 4, when dividing with $x^2 + 1$ have remainder 2x+3. Find remainder dividing polynomial with($x+1$)($x^2+1$)chinese remainder theorem proofChinese Remainder Theorem InterpretationChinese Remainder Theorem clarificationI can't use Chinese Remainder Theorem.Chinese Remainder Theorem for $xequiv 0 pmody$Comparing two statements of Chinese Remainder Theorem (Sun-Ze Theorem)Chinese remainder theorem methodChinese Remainder Theorem problem 7Chinese Remainder Theorem with 0 mod nSolve a system of congruences using the Chinese Remainder Theorem

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Adapting the Chinese Remainder Theorem (CRT) for integers to polynomials

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Adapting the Chinese Remainder Theorem (CRT) for integers to polynomials



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)mod Distributive Law, factoring $!!bmod!!:$ $ abbmod ac = a(bbmod c)$Remainder of polynomial by product of 2 polynomials$f$ dividing by $x + 1$ have remainder 4, when dividing with $x^2 + 1$ have remainder 2x+3. Find remainder dividing polynomial with($x+1$)($x^2+1$)chinese remainder theorem proofChinese Remainder Theorem InterpretationChinese Remainder Theorem clarificationI can't use Chinese Remainder Theorem.Chinese Remainder Theorem for $xequiv 0 pmody$Comparing two statements of Chinese Remainder Theorem (Sun-Ze Theorem)Chinese remainder theorem methodChinese Remainder Theorem problem 7Chinese Remainder Theorem with 0 mod nSolve a system of congruences using the Chinese Remainder Theorem










2












$begingroup$


I did a few examples using the CRT to solve congruences where everything was in terms of integers. I'm trying to use the same technique for polynomials over $mathbbQ$, but I'm getting stuck.




Here's an example with integers:



$begincasesx equiv 1 , (mathrmmod , 5) \
x equiv 2 , (mathrmmod , 7) \
x equiv 3 , (mathrmmod , 9) \
x equiv 4 , (mathrmmod , 11).
endcases$



Since all the moduli are pairwise relatively prime, we can use the CRT. Here's some notation I'm using:



$bullet , M$ denotes the product of the moduli (in this case, $M = 5 cdot7 cdot 9 cdot 11$)



$bullet , m_i $ denotes the modulus in the $i^mathrmth$ congruence



$bullet , M_i$ denotes $dfracMm_i$



$bullet , y_i$ denotes the inverse of $M_i$ (mod $m_i$), i.e. $y_i$ satisfies $y_i M_i equiv 1$ (mod $m_i$).



Then $x = displaystyle sum_i = 1^n a_iM_iy_i$, and this solution is unique (mod $M$).




Now I want to apply the same technique to the following:



$begincases
f(x) equiv 1 , (mathrm mod , x^2 + 1) \
f(x) equiv x , (mathrmmod , x^4),
endcases$



where $f(x) in mathbbQ(x)$. Having checked that the moduli are relatively prime, we should be able to use the CRT. Using the notation above, I have the following:



$M = (x^4)(x^2 + 1)$



$M_1 = x^4$



$M_2 = x^2 + 1$



Here's where I run into a problem. I need to find $y_1, y_2$ such that



$begincases
y_1 (x^4) equiv 1 , (mathrmmod , x^2 + 1) \
y_2 (x^2+1) equiv 1 , (mathrmmod , x^4).
endcases$



But how does one find $y_1, y_2$?










share|cite|improve this question









$endgroup$







  • 1




    $begingroup$
    "Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
    $endgroup$
    – kccu
    5 hours ago










  • $begingroup$
    Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
    $endgroup$
    – Junglemath
    4 hours ago















2












$begingroup$


I did a few examples using the CRT to solve congruences where everything was in terms of integers. I'm trying to use the same technique for polynomials over $mathbbQ$, but I'm getting stuck.




Here's an example with integers:



$begincasesx equiv 1 , (mathrmmod , 5) \
x equiv 2 , (mathrmmod , 7) \
x equiv 3 , (mathrmmod , 9) \
x equiv 4 , (mathrmmod , 11).
endcases$



Since all the moduli are pairwise relatively prime, we can use the CRT. Here's some notation I'm using:



$bullet , M$ denotes the product of the moduli (in this case, $M = 5 cdot7 cdot 9 cdot 11$)



$bullet , m_i $ denotes the modulus in the $i^mathrmth$ congruence



$bullet , M_i$ denotes $dfracMm_i$



$bullet , y_i$ denotes the inverse of $M_i$ (mod $m_i$), i.e. $y_i$ satisfies $y_i M_i equiv 1$ (mod $m_i$).



Then $x = displaystyle sum_i = 1^n a_iM_iy_i$, and this solution is unique (mod $M$).




Now I want to apply the same technique to the following:



$begincases
f(x) equiv 1 , (mathrm mod , x^2 + 1) \
f(x) equiv x , (mathrmmod , x^4),
endcases$



where $f(x) in mathbbQ(x)$. Having checked that the moduli are relatively prime, we should be able to use the CRT. Using the notation above, I have the following:



$M = (x^4)(x^2 + 1)$



$M_1 = x^4$



$M_2 = x^2 + 1$



Here's where I run into a problem. I need to find $y_1, y_2$ such that



$begincases
y_1 (x^4) equiv 1 , (mathrmmod , x^2 + 1) \
y_2 (x^2+1) equiv 1 , (mathrmmod , x^4).
endcases$



But how does one find $y_1, y_2$?










share|cite|improve this question









$endgroup$







  • 1




    $begingroup$
    "Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
    $endgroup$
    – kccu
    5 hours ago










  • $begingroup$
    Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
    $endgroup$
    – Junglemath
    4 hours ago













2












2








2





$begingroup$


I did a few examples using the CRT to solve congruences where everything was in terms of integers. I'm trying to use the same technique for polynomials over $mathbbQ$, but I'm getting stuck.




Here's an example with integers:



$begincasesx equiv 1 , (mathrmmod , 5) \
x equiv 2 , (mathrmmod , 7) \
x equiv 3 , (mathrmmod , 9) \
x equiv 4 , (mathrmmod , 11).
endcases$



Since all the moduli are pairwise relatively prime, we can use the CRT. Here's some notation I'm using:



$bullet , M$ denotes the product of the moduli (in this case, $M = 5 cdot7 cdot 9 cdot 11$)



$bullet , m_i $ denotes the modulus in the $i^mathrmth$ congruence



$bullet , M_i$ denotes $dfracMm_i$



$bullet , y_i$ denotes the inverse of $M_i$ (mod $m_i$), i.e. $y_i$ satisfies $y_i M_i equiv 1$ (mod $m_i$).



Then $x = displaystyle sum_i = 1^n a_iM_iy_i$, and this solution is unique (mod $M$).




Now I want to apply the same technique to the following:



$begincases
f(x) equiv 1 , (mathrm mod , x^2 + 1) \
f(x) equiv x , (mathrmmod , x^4),
endcases$



where $f(x) in mathbbQ(x)$. Having checked that the moduli are relatively prime, we should be able to use the CRT. Using the notation above, I have the following:



$M = (x^4)(x^2 + 1)$



$M_1 = x^4$



$M_2 = x^2 + 1$



Here's where I run into a problem. I need to find $y_1, y_2$ such that



$begincases
y_1 (x^4) equiv 1 , (mathrmmod , x^2 + 1) \
y_2 (x^2+1) equiv 1 , (mathrmmod , x^4).
endcases$



But how does one find $y_1, y_2$?










share|cite|improve this question









$endgroup$




I did a few examples using the CRT to solve congruences where everything was in terms of integers. I'm trying to use the same technique for polynomials over $mathbbQ$, but I'm getting stuck.




Here's an example with integers:



$begincasesx equiv 1 , (mathrmmod , 5) \
x equiv 2 , (mathrmmod , 7) \
x equiv 3 , (mathrmmod , 9) \
x equiv 4 , (mathrmmod , 11).
endcases$



Since all the moduli are pairwise relatively prime, we can use the CRT. Here's some notation I'm using:



$bullet , M$ denotes the product of the moduli (in this case, $M = 5 cdot7 cdot 9 cdot 11$)



$bullet , m_i $ denotes the modulus in the $i^mathrmth$ congruence



$bullet , M_i$ denotes $dfracMm_i$



$bullet , y_i$ denotes the inverse of $M_i$ (mod $m_i$), i.e. $y_i$ satisfies $y_i M_i equiv 1$ (mod $m_i$).



Then $x = displaystyle sum_i = 1^n a_iM_iy_i$, and this solution is unique (mod $M$).




Now I want to apply the same technique to the following:



$begincases
f(x) equiv 1 , (mathrm mod , x^2 + 1) \
f(x) equiv x , (mathrmmod , x^4),
endcases$



where $f(x) in mathbbQ(x)$. Having checked that the moduli are relatively prime, we should be able to use the CRT. Using the notation above, I have the following:



$M = (x^4)(x^2 + 1)$



$M_1 = x^4$



$M_2 = x^2 + 1$



Here's where I run into a problem. I need to find $y_1, y_2$ such that



$begincases
y_1 (x^4) equiv 1 , (mathrmmod , x^2 + 1) \
y_2 (x^2+1) equiv 1 , (mathrmmod , x^4).
endcases$



But how does one find $y_1, y_2$?







abstract-algebra ring-theory chinese-remainder-theorem






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked 5 hours ago









JunglemathJunglemath

6016




6016







  • 1




    $begingroup$
    "Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
    $endgroup$
    – kccu
    5 hours ago










  • $begingroup$
    Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
    $endgroup$
    – Junglemath
    4 hours ago












  • 1




    $begingroup$
    "Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
    $endgroup$
    – kccu
    5 hours ago










  • $begingroup$
    Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
    $endgroup$
    – Junglemath
    4 hours ago







1




1




$begingroup$
"Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
$endgroup$
– kccu
5 hours ago




$begingroup$
"Having checked that the moduli are relatively prime..." but that means precisely that there exist $p_1(x)$ and $p_2(x)$ such that $p_1(x)x^4 + p_2(x)(x^2+1)=1$.
$endgroup$
– kccu
5 hours ago












$begingroup$
Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
$endgroup$
– Junglemath
4 hours ago




$begingroup$
Are you saying that I can find $p_1(x)$ and $p_2(x)$ in general by using the extended Euclidean algorithm, and that $p_1(x)$ and $p_2(x)$ are precisely my $y_1$ and $y_2$?
$endgroup$
– Junglemath
4 hours ago










2 Answers
2






active

oldest

votes


















3












$begingroup$

To find $y_1$ and $y_2$ consider solving the problem
$$y_1x^4+y_2(x^2+1)=1.$$
This is not always easy to solve, but in this case a solution comes to mind. Note that by difference of squares
$$(x^2-1)(x^2+1)=x^4-1,$$
hence
$$x^4+[(-1)(x^2-1)](x^2+1)=1.$$
This tells us that we can choose
$$y_1=1,$$
$$y_2=(1-x^2).$$






share|cite|improve this answer











$endgroup$












  • $begingroup$
    Is there an algorithmic way of solving these, rather than relying on intuition?
    $endgroup$
    – Junglemath
    4 hours ago










  • $begingroup$
    @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
    $endgroup$
    – Paolo
    4 hours ago







  • 1




    $begingroup$
    @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
    $endgroup$
    – Melody
    4 hours ago







  • 1




    $begingroup$
    @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
    $endgroup$
    – Melody
    4 hours ago







  • 1




    $begingroup$
    @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
    $endgroup$
    – Bill Dubuque
    3 hours ago



















1












$begingroup$

Bu applying $ abbmod ac, =, a(bbmod c) $ [Mod Distributive Law] $ $ it is a bit simpler:



$ f-x,bmod, x^large 4(x^large 2!+!1), =, x^large 4underbraceleft[dfraccolor#c00f-xcolor#0a0x^large 4bmod x^large 2!+!1right]_large color#0a0x^Large 4 equiv 1 rm by x^Large 2 equiv -1 =, x^large 4[1-x], $ by $,color#c00fequiv 1pmod!x^large 2!+!1$



Remark $ $ Here are further examples done using MDL (an operational form of CRT).



You can find further details here on transforming the Bezout equation into a CRT solution (the method sketched in Melody's answer).






share|cite|improve this answer











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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    3












    $begingroup$

    To find $y_1$ and $y_2$ consider solving the problem
    $$y_1x^4+y_2(x^2+1)=1.$$
    This is not always easy to solve, but in this case a solution comes to mind. Note that by difference of squares
    $$(x^2-1)(x^2+1)=x^4-1,$$
    hence
    $$x^4+[(-1)(x^2-1)](x^2+1)=1.$$
    This tells us that we can choose
    $$y_1=1,$$
    $$y_2=(1-x^2).$$






    share|cite|improve this answer











    $endgroup$












    • $begingroup$
      Is there an algorithmic way of solving these, rather than relying on intuition?
      $endgroup$
      – Junglemath
      4 hours ago










    • $begingroup$
      @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
      $endgroup$
      – Paolo
      4 hours ago







    • 1




      $begingroup$
      @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
      $endgroup$
      – Bill Dubuque
      3 hours ago
















    3












    $begingroup$

    To find $y_1$ and $y_2$ consider solving the problem
    $$y_1x^4+y_2(x^2+1)=1.$$
    This is not always easy to solve, but in this case a solution comes to mind. Note that by difference of squares
    $$(x^2-1)(x^2+1)=x^4-1,$$
    hence
    $$x^4+[(-1)(x^2-1)](x^2+1)=1.$$
    This tells us that we can choose
    $$y_1=1,$$
    $$y_2=(1-x^2).$$






    share|cite|improve this answer











    $endgroup$












    • $begingroup$
      Is there an algorithmic way of solving these, rather than relying on intuition?
      $endgroup$
      – Junglemath
      4 hours ago










    • $begingroup$
      @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
      $endgroup$
      – Paolo
      4 hours ago







    • 1




      $begingroup$
      @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
      $endgroup$
      – Bill Dubuque
      3 hours ago














    3












    3








    3





    $begingroup$

    To find $y_1$ and $y_2$ consider solving the problem
    $$y_1x^4+y_2(x^2+1)=1.$$
    This is not always easy to solve, but in this case a solution comes to mind. Note that by difference of squares
    $$(x^2-1)(x^2+1)=x^4-1,$$
    hence
    $$x^4+[(-1)(x^2-1)](x^2+1)=1.$$
    This tells us that we can choose
    $$y_1=1,$$
    $$y_2=(1-x^2).$$






    share|cite|improve this answer











    $endgroup$



    To find $y_1$ and $y_2$ consider solving the problem
    $$y_1x^4+y_2(x^2+1)=1.$$
    This is not always easy to solve, but in this case a solution comes to mind. Note that by difference of squares
    $$(x^2-1)(x^2+1)=x^4-1,$$
    hence
    $$x^4+[(-1)(x^2-1)](x^2+1)=1.$$
    This tells us that we can choose
    $$y_1=1,$$
    $$y_2=(1-x^2).$$







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited 4 hours ago

























    answered 5 hours ago









    MelodyMelody

    1,42212




    1,42212











    • $begingroup$
      Is there an algorithmic way of solving these, rather than relying on intuition?
      $endgroup$
      – Junglemath
      4 hours ago










    • $begingroup$
      @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
      $endgroup$
      – Paolo
      4 hours ago







    • 1




      $begingroup$
      @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
      $endgroup$
      – Bill Dubuque
      3 hours ago

















    • $begingroup$
      Is there an algorithmic way of solving these, rather than relying on intuition?
      $endgroup$
      – Junglemath
      4 hours ago










    • $begingroup$
      @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
      $endgroup$
      – Paolo
      4 hours ago







    • 1




      $begingroup$
      @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
      $endgroup$
      – Melody
      4 hours ago







    • 1




      $begingroup$
      @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
      $endgroup$
      – Bill Dubuque
      3 hours ago
















    $begingroup$
    Is there an algorithmic way of solving these, rather than relying on intuition?
    $endgroup$
    – Junglemath
    4 hours ago




    $begingroup$
    Is there an algorithmic way of solving these, rather than relying on intuition?
    $endgroup$
    – Junglemath
    4 hours ago












    $begingroup$
    @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
    $endgroup$
    – Paolo
    4 hours ago





    $begingroup$
    @Junglemath By Euclidean algorithm you can find two polynomials $p(x), q(x) in mathbbQ[x]$ such that $p(x) x^4 + q(x) (x^2 + 1) = 1$.
    $endgroup$
    – Paolo
    4 hours ago





    1




    1




    $begingroup$
    @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
    $endgroup$
    – Melody
    4 hours ago





    $begingroup$
    @Junglemath The polynomials over a field form a Euclidean Domain, so yes, there is. If the gcd of $f_1,f_2inmathbbQ[x]$ is a unit, then you can perform the Euclidean Algorithm to find their gcd. Now, you can reverse the algorithm to write them as a linear combination of their gcd the same way you would for integers. I said not easy, because the process can be time consuming and very tedious.
    $endgroup$
    – Melody
    4 hours ago





    1




    1




    $begingroup$
    @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
    $endgroup$
    – Melody
    4 hours ago





    $begingroup$
    @Junglemath I didn't really convert it. I knew in advanced the single equation had a solution. This is because $x^4$ and $x^2+1$ have no common roots, hence no common irreducible factors. This means they are relatively prime, in which case we can write $1$ as a linear combination. Knowing that, I knew solving the single equation would give rise to a solution to the congruence equations. This is completely analogous to how you can solve everything over the integers.
    $endgroup$
    – Melody
    4 hours ago





    1




    1




    $begingroup$
    @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
    $endgroup$
    – Bill Dubuque
    3 hours ago





    $begingroup$
    @Junglemath I describe here at length this method of scaling the Bezout equation into a CRT solution.
    $endgroup$
    – Bill Dubuque
    3 hours ago












    1












    $begingroup$

    Bu applying $ abbmod ac, =, a(bbmod c) $ [Mod Distributive Law] $ $ it is a bit simpler:



    $ f-x,bmod, x^large 4(x^large 2!+!1), =, x^large 4underbraceleft[dfraccolor#c00f-xcolor#0a0x^large 4bmod x^large 2!+!1right]_large color#0a0x^Large 4 equiv 1 rm by x^Large 2 equiv -1 =, x^large 4[1-x], $ by $,color#c00fequiv 1pmod!x^large 2!+!1$



    Remark $ $ Here are further examples done using MDL (an operational form of CRT).



    You can find further details here on transforming the Bezout equation into a CRT solution (the method sketched in Melody's answer).






    share|cite|improve this answer











    $endgroup$

















      1












      $begingroup$

      Bu applying $ abbmod ac, =, a(bbmod c) $ [Mod Distributive Law] $ $ it is a bit simpler:



      $ f-x,bmod, x^large 4(x^large 2!+!1), =, x^large 4underbraceleft[dfraccolor#c00f-xcolor#0a0x^large 4bmod x^large 2!+!1right]_large color#0a0x^Large 4 equiv 1 rm by x^Large 2 equiv -1 =, x^large 4[1-x], $ by $,color#c00fequiv 1pmod!x^large 2!+!1$



      Remark $ $ Here are further examples done using MDL (an operational form of CRT).



      You can find further details here on transforming the Bezout equation into a CRT solution (the method sketched in Melody's answer).






      share|cite|improve this answer











      $endgroup$















        1












        1








        1





        $begingroup$

        Bu applying $ abbmod ac, =, a(bbmod c) $ [Mod Distributive Law] $ $ it is a bit simpler:



        $ f-x,bmod, x^large 4(x^large 2!+!1), =, x^large 4underbraceleft[dfraccolor#c00f-xcolor#0a0x^large 4bmod x^large 2!+!1right]_large color#0a0x^Large 4 equiv 1 rm by x^Large 2 equiv -1 =, x^large 4[1-x], $ by $,color#c00fequiv 1pmod!x^large 2!+!1$



        Remark $ $ Here are further examples done using MDL (an operational form of CRT).



        You can find further details here on transforming the Bezout equation into a CRT solution (the method sketched in Melody's answer).






        share|cite|improve this answer











        $endgroup$



        Bu applying $ abbmod ac, =, a(bbmod c) $ [Mod Distributive Law] $ $ it is a bit simpler:



        $ f-x,bmod, x^large 4(x^large 2!+!1), =, x^large 4underbraceleft[dfraccolor#c00f-xcolor#0a0x^large 4bmod x^large 2!+!1right]_large color#0a0x^Large 4 equiv 1 rm by x^Large 2 equiv -1 =, x^large 4[1-x], $ by $,color#c00fequiv 1pmod!x^large 2!+!1$



        Remark $ $ Here are further examples done using MDL (an operational form of CRT).



        You can find further details here on transforming the Bezout equation into a CRT solution (the method sketched in Melody's answer).







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited 2 hours ago

























        answered 3 hours ago









        Bill DubuqueBill Dubuque

        214k29198660




        214k29198660



























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