Degenerate kernel method to solve Fredholm integral equation of the second kind
$begingroup$
$$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
$$
I have this fredholm integral equation of the second kind and am not sure how to answer this equation.
I know that is has to be written in the form
$$ sum a_jx^{j-1} $$
I do not know how to integrate with the function $f(y)$ in the integral.
Any help would be appreciated.
Thanks
calculus linear-algebra integration integral-equations
$endgroup$
add a comment |
$begingroup$
$$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
$$
I have this fredholm integral equation of the second kind and am not sure how to answer this equation.
I know that is has to be written in the form
$$ sum a_jx^{j-1} $$
I do not know how to integrate with the function $f(y)$ in the integral.
Any help would be appreciated.
Thanks
calculus linear-algebra integration integral-equations
$endgroup$
add a comment |
$begingroup$
$$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
$$
I have this fredholm integral equation of the second kind and am not sure how to answer this equation.
I know that is has to be written in the form
$$ sum a_jx^{j-1} $$
I do not know how to integrate with the function $f(y)$ in the integral.
Any help would be appreciated.
Thanks
calculus linear-algebra integration integral-equations
$endgroup$
$$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
$$
I have this fredholm integral equation of the second kind and am not sure how to answer this equation.
I know that is has to be written in the form
$$ sum a_jx^{j-1} $$
I do not know how to integrate with the function $f(y)$ in the integral.
Any help would be appreciated.
Thanks
calculus linear-algebra integration integral-equations
calculus linear-algebra integration integral-equations
edited Dec 9 '18 at 19:27
p s
asked Dec 2 '18 at 16:02
p sp s
358
358
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
can you start with:
$$f(x)+int_0^1(xy+x^2y^2)f(y)dy=x^3+frac16x^2+frac15x$$
$$f'(x)+(x+x^2)f(1)=3x^2+frac13x+frac15$$
$$f'(x)=(3-f(1))x^2+left(frac13-f(1)right)+frac15$$
so:
$$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$
$endgroup$
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
add a comment |
$begingroup$
Note that we can write the equation as
$$ f(x) = x^3 + left[frac{1}{6} - int limits_0^1 y^2 f(y) , mathrm{d} yright] x^2 + left[frac{1}{5} - int limits_0^1 y f(y) , mathrm{d} yright] x , , , x in [0,1] , . $$
Obviously, we do not know the values of the integrals yet, but it turns out that we do not need to! It is sufficient to conclude that there are constants $a, b in mathbb{R}$ such that
$$ f(x) = x^3 + a x^2 + b x , , , x in [0,1] , . $$
We can then plug this form of $f$ into the previous equation and compute the integrals to obtain
$$ x^3 + a x^2 + b x = x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
This yields the linear system
$$ begin{pmatrix} frac{6}{5} && frac{1}{4}\ frac{1}{4} && frac{4}{3} end{pmatrix} begin{pmatrix} a \b end{pmatrix} = begin{pmatrix} 0 \0 end{pmatrix} , ,$$
which only has the trivial solution $a=b=0$ . Therefore
$$ f(x) = x^3 , , , x in [0,1] , , $$
is the unique solution to the integral equation.
$endgroup$
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
add a comment |
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2 Answers
2
active
oldest
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2 Answers
2
active
oldest
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active
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votes
$begingroup$
can you start with:
$$f(x)+int_0^1(xy+x^2y^2)f(y)dy=x^3+frac16x^2+frac15x$$
$$f'(x)+(x+x^2)f(1)=3x^2+frac13x+frac15$$
$$f'(x)=(3-f(1))x^2+left(frac13-f(1)right)+frac15$$
so:
$$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$
$endgroup$
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
add a comment |
$begingroup$
can you start with:
$$f(x)+int_0^1(xy+x^2y^2)f(y)dy=x^3+frac16x^2+frac15x$$
$$f'(x)+(x+x^2)f(1)=3x^2+frac13x+frac15$$
$$f'(x)=(3-f(1))x^2+left(frac13-f(1)right)+frac15$$
so:
$$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$
$endgroup$
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
add a comment |
$begingroup$
can you start with:
$$f(x)+int_0^1(xy+x^2y^2)f(y)dy=x^3+frac16x^2+frac15x$$
$$f'(x)+(x+x^2)f(1)=3x^2+frac13x+frac15$$
$$f'(x)=(3-f(1))x^2+left(frac13-f(1)right)+frac15$$
so:
$$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$
$endgroup$
can you start with:
$$f(x)+int_0^1(xy+x^2y^2)f(y)dy=x^3+frac16x^2+frac15x$$
$$f'(x)+(x+x^2)f(1)=3x^2+frac13x+frac15$$
$$f'(x)=(3-f(1))x^2+left(frac13-f(1)right)+frac15$$
so:
$$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$
answered Dec 2 '18 at 18:22
Henry LeeHenry Lee
1,865219
1,865219
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
add a comment |
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
Once integrating that final integral would it be able to write it as a sum of a function. Also, how would I integrate f(1)
$endgroup$
– p s
Dec 2 '18 at 21:00
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
$begingroup$
f(1) is just a constant, but we would need a way to work out its value, which is an issue as the function is defined with the function itself
$endgroup$
– Henry Lee
Dec 2 '18 at 21:02
add a comment |
$begingroup$
Note that we can write the equation as
$$ f(x) = x^3 + left[frac{1}{6} - int limits_0^1 y^2 f(y) , mathrm{d} yright] x^2 + left[frac{1}{5} - int limits_0^1 y f(y) , mathrm{d} yright] x , , , x in [0,1] , . $$
Obviously, we do not know the values of the integrals yet, but it turns out that we do not need to! It is sufficient to conclude that there are constants $a, b in mathbb{R}$ such that
$$ f(x) = x^3 + a x^2 + b x , , , x in [0,1] , . $$
We can then plug this form of $f$ into the previous equation and compute the integrals to obtain
$$ x^3 + a x^2 + b x = x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
This yields the linear system
$$ begin{pmatrix} frac{6}{5} && frac{1}{4}\ frac{1}{4} && frac{4}{3} end{pmatrix} begin{pmatrix} a \b end{pmatrix} = begin{pmatrix} 0 \0 end{pmatrix} , ,$$
which only has the trivial solution $a=b=0$ . Therefore
$$ f(x) = x^3 , , , x in [0,1] , , $$
is the unique solution to the integral equation.
$endgroup$
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
add a comment |
$begingroup$
Note that we can write the equation as
$$ f(x) = x^3 + left[frac{1}{6} - int limits_0^1 y^2 f(y) , mathrm{d} yright] x^2 + left[frac{1}{5} - int limits_0^1 y f(y) , mathrm{d} yright] x , , , x in [0,1] , . $$
Obviously, we do not know the values of the integrals yet, but it turns out that we do not need to! It is sufficient to conclude that there are constants $a, b in mathbb{R}$ such that
$$ f(x) = x^3 + a x^2 + b x , , , x in [0,1] , . $$
We can then plug this form of $f$ into the previous equation and compute the integrals to obtain
$$ x^3 + a x^2 + b x = x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
This yields the linear system
$$ begin{pmatrix} frac{6}{5} && frac{1}{4}\ frac{1}{4} && frac{4}{3} end{pmatrix} begin{pmatrix} a \b end{pmatrix} = begin{pmatrix} 0 \0 end{pmatrix} , ,$$
which only has the trivial solution $a=b=0$ . Therefore
$$ f(x) = x^3 , , , x in [0,1] , , $$
is the unique solution to the integral equation.
$endgroup$
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
add a comment |
$begingroup$
Note that we can write the equation as
$$ f(x) = x^3 + left[frac{1}{6} - int limits_0^1 y^2 f(y) , mathrm{d} yright] x^2 + left[frac{1}{5} - int limits_0^1 y f(y) , mathrm{d} yright] x , , , x in [0,1] , . $$
Obviously, we do not know the values of the integrals yet, but it turns out that we do not need to! It is sufficient to conclude that there are constants $a, b in mathbb{R}$ such that
$$ f(x) = x^3 + a x^2 + b x , , , x in [0,1] , . $$
We can then plug this form of $f$ into the previous equation and compute the integrals to obtain
$$ x^3 + a x^2 + b x = x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
This yields the linear system
$$ begin{pmatrix} frac{6}{5} && frac{1}{4}\ frac{1}{4} && frac{4}{3} end{pmatrix} begin{pmatrix} a \b end{pmatrix} = begin{pmatrix} 0 \0 end{pmatrix} , ,$$
which only has the trivial solution $a=b=0$ . Therefore
$$ f(x) = x^3 , , , x in [0,1] , , $$
is the unique solution to the integral equation.
$endgroup$
Note that we can write the equation as
$$ f(x) = x^3 + left[frac{1}{6} - int limits_0^1 y^2 f(y) , mathrm{d} yright] x^2 + left[frac{1}{5} - int limits_0^1 y f(y) , mathrm{d} yright] x , , , x in [0,1] , . $$
Obviously, we do not know the values of the integrals yet, but it turns out that we do not need to! It is sufficient to conclude that there are constants $a, b in mathbb{R}$ such that
$$ f(x) = x^3 + a x^2 + b x , , , x in [0,1] , . $$
We can then plug this form of $f$ into the previous equation and compute the integrals to obtain
$$ x^3 + a x^2 + b x = x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
This yields the linear system
$$ begin{pmatrix} frac{6}{5} && frac{1}{4}\ frac{1}{4} && frac{4}{3} end{pmatrix} begin{pmatrix} a \b end{pmatrix} = begin{pmatrix} 0 \0 end{pmatrix} , ,$$
which only has the trivial solution $a=b=0$ . Therefore
$$ f(x) = x^3 , , , x in [0,1] , , $$
is the unique solution to the integral equation.
answered Dec 2 '18 at 22:57
ComplexYetTrivialComplexYetTrivial
3,7302629
3,7302629
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
add a comment |
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
Thank you, this gives me a final answer but I have to write it as a sum of functions in the form $$ sum a_jx^{j-1} $$ how would I change what you have solved above into this format?
$endgroup$
– p s
Dec 2 '18 at 23:22
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
@ps You can write $f(x) = x^3 = sum_{j=2}^4 a_j x^{j-1} $ with $a_4 = 1$ and $a_3 = a_2 = 0$ .
$endgroup$
– ComplexYetTrivial
Dec 2 '18 at 23:32
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
$begingroup$
how did you get to $$ x^3 - left(frac{a}{5}+frac{b}{4}right) x^2 - left(frac{a}{4}+frac{b}{3}right)x , , , x in [0,1] , . $$
$endgroup$
– p s
Dec 9 '18 at 19:00
add a comment |
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