Construct a polynomial $p$ of degree $leq n-1$ such that $p(a_i) = b_i$
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Theorem. Given two countably infinite sequences of complex numbers ${a_{n}}_{n}$ and ${b_{n}}_{n}$ with $lim_{n to infty}|a_{n}| = infty$, it is always possible to find a entire function $F$ that satisfies $F(a_{n}) = b_{n}$ for all $n$.
First, I want to prove
Problem. If $a_1,dots,a_n$ and $b_1,dots,b_n$ are distinct complex numbers, I can construct a polynomial $p$ of degree $leq n-1$ such that $p(a_i) = b_i$ for all $i=1,dots,n$.
My approach.
$$c_{0} + c_{1}a_{1} + c_{2}a_{1}^{2} + cdots + c_{n-1}a_{1}^{n-1} = b_{1}$$
$$c_{0} + c_{1}a_{2} + c_{2}a_{2}^{2} + cdots + c_{n-1}a_{2}^{n-1} = b_{2}$$
$$vdots$$
$$c_{0} + c_{1}a_{n} + c_{2}a_{n}^{2} + cdots + c_{n-1}a_{n}^{n-1} = b_{n}$$
and so
$$left(begin{array}{ccccc}
1 & a_{1} & a_{1}^{2} & cdots & a_{1}^{n-1}\
1 & a_{2} & a_{2}^{2} & cdots & a_{2}^{n-1}\
vdots & vdots & vdots & ddots & vdots\
1 & a_{n} & a_{n}^{2} & cdots & a_{n}^{n-1}\
end{array}right)
left(begin{array}{c}
c_{0}\
c_{1}\
vdots\
c_{n-1}
end{array}right)
=
left(begin{array}{c}
b_{1}\
b_{2}\
vdots\
b_{n}
end{array}right)$$
What is the best method to solve this system? Or, Is there a better approach to this problem??
complex-analysis interpolation
|
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up vote
1
down vote
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Theorem. Given two countably infinite sequences of complex numbers ${a_{n}}_{n}$ and ${b_{n}}_{n}$ with $lim_{n to infty}|a_{n}| = infty$, it is always possible to find a entire function $F$ that satisfies $F(a_{n}) = b_{n}$ for all $n$.
First, I want to prove
Problem. If $a_1,dots,a_n$ and $b_1,dots,b_n$ are distinct complex numbers, I can construct a polynomial $p$ of degree $leq n-1$ such that $p(a_i) = b_i$ for all $i=1,dots,n$.
My approach.
$$c_{0} + c_{1}a_{1} + c_{2}a_{1}^{2} + cdots + c_{n-1}a_{1}^{n-1} = b_{1}$$
$$c_{0} + c_{1}a_{2} + c_{2}a_{2}^{2} + cdots + c_{n-1}a_{2}^{n-1} = b_{2}$$
$$vdots$$
$$c_{0} + c_{1}a_{n} + c_{2}a_{n}^{2} + cdots + c_{n-1}a_{n}^{n-1} = b_{n}$$
and so
$$left(begin{array}{ccccc}
1 & a_{1} & a_{1}^{2} & cdots & a_{1}^{n-1}\
1 & a_{2} & a_{2}^{2} & cdots & a_{2}^{n-1}\
vdots & vdots & vdots & ddots & vdots\
1 & a_{n} & a_{n}^{2} & cdots & a_{n}^{n-1}\
end{array}right)
left(begin{array}{c}
c_{0}\
c_{1}\
vdots\
c_{n-1}
end{array}right)
=
left(begin{array}{c}
b_{1}\
b_{2}\
vdots\
b_{n}
end{array}right)$$
What is the best method to solve this system? Or, Is there a better approach to this problem??
complex-analysis interpolation
2
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
2
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
1
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54
|
show 1 more comment
up vote
1
down vote
favorite
up vote
1
down vote
favorite
Theorem. Given two countably infinite sequences of complex numbers ${a_{n}}_{n}$ and ${b_{n}}_{n}$ with $lim_{n to infty}|a_{n}| = infty$, it is always possible to find a entire function $F$ that satisfies $F(a_{n}) = b_{n}$ for all $n$.
First, I want to prove
Problem. If $a_1,dots,a_n$ and $b_1,dots,b_n$ are distinct complex numbers, I can construct a polynomial $p$ of degree $leq n-1$ such that $p(a_i) = b_i$ for all $i=1,dots,n$.
My approach.
$$c_{0} + c_{1}a_{1} + c_{2}a_{1}^{2} + cdots + c_{n-1}a_{1}^{n-1} = b_{1}$$
$$c_{0} + c_{1}a_{2} + c_{2}a_{2}^{2} + cdots + c_{n-1}a_{2}^{n-1} = b_{2}$$
$$vdots$$
$$c_{0} + c_{1}a_{n} + c_{2}a_{n}^{2} + cdots + c_{n-1}a_{n}^{n-1} = b_{n}$$
and so
$$left(begin{array}{ccccc}
1 & a_{1} & a_{1}^{2} & cdots & a_{1}^{n-1}\
1 & a_{2} & a_{2}^{2} & cdots & a_{2}^{n-1}\
vdots & vdots & vdots & ddots & vdots\
1 & a_{n} & a_{n}^{2} & cdots & a_{n}^{n-1}\
end{array}right)
left(begin{array}{c}
c_{0}\
c_{1}\
vdots\
c_{n-1}
end{array}right)
=
left(begin{array}{c}
b_{1}\
b_{2}\
vdots\
b_{n}
end{array}right)$$
What is the best method to solve this system? Or, Is there a better approach to this problem??
complex-analysis interpolation
Theorem. Given two countably infinite sequences of complex numbers ${a_{n}}_{n}$ and ${b_{n}}_{n}$ with $lim_{n to infty}|a_{n}| = infty$, it is always possible to find a entire function $F$ that satisfies $F(a_{n}) = b_{n}$ for all $n$.
First, I want to prove
Problem. If $a_1,dots,a_n$ and $b_1,dots,b_n$ are distinct complex numbers, I can construct a polynomial $p$ of degree $leq n-1$ such that $p(a_i) = b_i$ for all $i=1,dots,n$.
My approach.
$$c_{0} + c_{1}a_{1} + c_{2}a_{1}^{2} + cdots + c_{n-1}a_{1}^{n-1} = b_{1}$$
$$c_{0} + c_{1}a_{2} + c_{2}a_{2}^{2} + cdots + c_{n-1}a_{2}^{n-1} = b_{2}$$
$$vdots$$
$$c_{0} + c_{1}a_{n} + c_{2}a_{n}^{2} + cdots + c_{n-1}a_{n}^{n-1} = b_{n}$$
and so
$$left(begin{array}{ccccc}
1 & a_{1} & a_{1}^{2} & cdots & a_{1}^{n-1}\
1 & a_{2} & a_{2}^{2} & cdots & a_{2}^{n-1}\
vdots & vdots & vdots & ddots & vdots\
1 & a_{n} & a_{n}^{2} & cdots & a_{n}^{n-1}\
end{array}right)
left(begin{array}{c}
c_{0}\
c_{1}\
vdots\
c_{n-1}
end{array}right)
=
left(begin{array}{c}
b_{1}\
b_{2}\
vdots\
b_{n}
end{array}right)$$
What is the best method to solve this system? Or, Is there a better approach to this problem??
complex-analysis interpolation
complex-analysis interpolation
asked Nov 19 at 3:44
Lucas Corrêa
1,252321
1,252321
2
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
2
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
1
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54
|
show 1 more comment
2
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
2
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
1
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54
2
2
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
2
2
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
1
1
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54
|
show 1 more comment
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2
This is called lagrange interpolation.
– Robert Wolfe
Nov 19 at 3:45
@RobertWolfe, thank you!
– Lucas Corrêa
Nov 19 at 3:49
2
Just like magic - if you the name of something, you gain power.
– marty cohen
Nov 19 at 4:20
1
For the main question see "An Interpoation Problem' in Rudin's RCA. [ Chapter on Zeros of Holomorphic Functions].
– Kavi Rama Murthy
Nov 19 at 5:28
@martycohen, absolutely! hahaha
– Lucas Corrêa
Nov 19 at 16:54