Degenerate kernel method to solve Fredholm integral equation of the second kind












2












$begingroup$


$$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
$$



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










share|cite|improve this question











$endgroup$

















    2












    $begingroup$


    $$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
    $$



    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










    share|cite|improve this question











    $endgroup$















      2












      2








      2


      0



      $begingroup$


      $$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
      $$



      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










      share|cite|improve this question











      $endgroup$




      $$ f(x) + int_0^1 (xy+x^2y^2) f(y) dy = x^3 +frac16x^2+ frac15x
      $$



      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






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      share|cite|improve this question













      share|cite|improve this question




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      edited Dec 9 '18 at 19:27







      p s

















      asked Dec 2 '18 at 16:02









      p sp s

      358




      358






















          2 Answers
          2






          active

          oldest

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          0












          $begingroup$

          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:
          $$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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



















          0












          $begingroup$

          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.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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













          Your Answer





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          2 Answers
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          2 Answers
          2






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          0












          $begingroup$

          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:
          $$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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
















          0












          $begingroup$

          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:
          $$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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














          0












          0








          0





          $begingroup$

          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:
          $$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$






          share|cite|improve this answer









          $endgroup$



          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:
          $$f(x)=intleft[(3-f(1))x^2+left(frac13-f(1)right)+frac15right]dx+C$$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          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


















          • $begingroup$
            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











          0












          $begingroup$

          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.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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


















          0












          $begingroup$

          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.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            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
















          0












          0








          0





          $begingroup$

          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.






          share|cite|improve this answer









          $endgroup$



          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.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          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




















          • $begingroup$
            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




















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