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A Linear Algebra Problem Related to Legendre Polynomials Scott Cameron Dalhousie University, Halifax, Nova Scotia, Canada June 27, 2018 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials Introduction: Statement of the


  1. I continued for a few more degrees, and the pattern continued as well. I thought maybe it is somehow possible that I made a mistake that only appears for odd degrees, so I checked if the answer held up with the original problem. I asked Maple for a random polynomial of degree ≤ 3, and integrated it against f ( x ) = − 15 x 2 + 15 x − 3 2 . The answer was the random polynomial at x = 1 2 . Perhaps no mistake was made. But why is this happening? To answer this we will state the question again, but in more general terms. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  2. • Generalizing the Problem Find f n ( x ) such that � 1 g ( c ) = f n ( x ) g ( x ) dx 0 where g ( x ) and f n ( x ) are polynomials of degree ≤ n . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  3. • Generalizing the Problem Find f n ( x ) such that � 1 g ( c ) = f n ( x ) g ( x ) dx 0 where g ( x ) and f n ( x ) are polynomials of degree ≤ n . Now let us write our question in terms of the following proposition. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  4. Proposition Let f n ( x ) be as previously defined. Then when c = 1 2 we have f 2 m + 1 ( x ) = f 2 m ( x ) for m ∈ N . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  5. Proposition Let f n ( x ) be as previously defined. Then when c = 1 2 we have f 2 m + 1 ( x ) = f 2 m ( x ) for m ∈ N . So then let n � a k x k f n ( x ) = k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  6. Proposition Let f n ( x ) be as previously defined. Then when c = 1 2 we have f 2 m + 1 ( x ) = f 2 m ( x ) for m ∈ N . So then let n � a k x k f n ( x ) = k = 0 and n � b k x k g ( x ) = k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  7. Proposition Let f n ( x ) be as previously defined. Then when c = 1 2 we have f 2 m + 1 ( x ) = f 2 m ( x ) for m ∈ N . So then let n � a k x k f n ( x ) = k = 0 and n � b k x k g ( x ) = k = 0 Solving in the same manner leads to Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  8.  1 1 1  1 . . .     a 0 1 2 3 n + 1 1 1 1 1 . . . a 1 c       2 3 4 n + 2   1 1 1 1    c 2  a 2  . . .  =     3 4 5 n + 3    .   .  . . . . ...   . . . . . .     . . . . . .         c n 1 1 1 1 a n . . . n + 1 n + 2 n + 3 2 n + 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  9.  1 1 1  1 . . .     a 0 1 2 3 n + 1 1 1 1 1 . . . a 1 c       2 3 4 n + 2   1 1 1 1    c 2  a 2  . . .  =     3 4 5 n + 3    .   .  . . . . ...   . . . . . .     . . . . . .         c n 1 1 1 1 a n . . . n + 1 n + 2 n + 3 2 n + 1 Now write this as Ha = c . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  10.  1 1 1  1 . . .     a 0 1 2 3 n + 1 1 1 1 1 . . . a 1 c       2 3 4 n + 2   1 1 1 1    c 2  a 2  . . .  =     3 4 5 n + 3    .   .  . . . . ...   . . . . . .     . . . . . .         c n 1 1 1 1 a n . . . n + 1 n + 2 n + 3 2 n + 1 Now write this as Ha = c . 1 The choice of H is because matrices of this form ( H i , j = i + j − 1 ) are known as Hilbert matrices. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  11. To continue we need to know the inverse of the matrix H. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  12. To continue we need to know the inverse of the matrix H. Luckily Hilbert matrices have a known formula for the entries of their inverse. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  13. To continue we need to know the inverse of the matrix H. Luckily Hilbert matrices have a known formula for the entries of their inverse. � n + i �� n + j � 2 �� i + j − 2 ( H i , j ) − 1 = ( − 1 ) i + j − 1 ( i + j − 1 ) . i + j − 1 i + j − 1 i − 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  14. To continue we need to know the inverse of the matrix H. Luckily Hilbert matrices have a known formula for the entries of their inverse. � n + i �� n + j � 2 �� i + j − 2 ( H i , j ) − 1 = ( − 1 ) i + j − 1 ( i + j − 1 ) . i + j − 1 i + j − 1 i − 1 Before continuing we need a definition. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  15. Definition Let h n , i ( c ) be the polynomial created by taking the dot product of the i th row of H − 1 and c . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  16. Definition Let h n , i ( c ) be the polynomial created by taking the dot product of the i th row of H − 1 and c . These polynomials determine the coefficients of f n ( x ) . That is, n + 1 � h n , k ( c ) x k − 1 h n , i ( c ) = a i − 1 , or f n ( x ) = k = 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  17. Definition Let h n , i ( c ) be the polynomial created by taking the dot product of the i th row of H − 1 and c . These polynomials determine the coefficients of f n ( x ) . That is, n + 1 � h n , k ( c ) x k − 1 h n , i ( c ) = a i − 1 , or f n ( x ) = k = 1 Let’s do an example to clarify. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  18. Example: If n = 2, then 1 1  1  2 3 1 1 1  . H =  2 3 4 1 1 1 3 4 5 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  19. Example: If n = 2, then 1 1  1  2 3 1 1 1  . H =  2 3 4 1 1 1 3 4 5 Using our formula,   9 − 36 30 H − 1 =  . − 36 192 − 180  30 − 180 180 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  20. Example: If n = 2, then 1 1  1  2 3 1 1 1  . H =  2 3 4 1 1 1 3 4 5 Using our formula,   9 − 36 30 H − 1 =  . − 36 192 − 180  30 − 180 180 So we have n = 2 and can see that 1 ≤ i ≤ 3. Thus h 2 , 1 ( c ) = 9 − 36 c + 30 c 2 , h 2 , 2 ( c ) = − 36 + 192 c − 180 c 2 , h 2 , 3 ( c ) = 30 − 180 c + 180 c 2 , f n ( x ) = h 2 , 1 ( c ) + h 2 , 2 ( c ) x + h 2 , 3 ( c ) x 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  21. Now back to our problem. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  22. Now back to our problem. If n is odd, and f n ( x ) = f n − 1 ( x ) when c = 1 2 , then the degree of f n ( x ) is n − 1. This means that a n = 0 in f n ( x ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  23. Now back to our problem. If n is odd, and f n ( x ) = f n − 1 ( x ) when c = 1 2 , then the degree of f n ( x ) is n − 1. This means that a n = 0 in f n ( x ) . This would correspond to the polynomial formed by the bottom row of H − 1 having a root at c = 1 2 . Using our definition, this can be written as h n , n + 1 ( c ) having a root at c = 1 2 . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  24. Now back to our problem. If n is odd, and f n ( x ) = f n − 1 ( x ) when c = 1 2 , then the degree of f n ( x ) is n − 1. This means that a n = 0 in f n ( x ) . This would correspond to the polynomial formed by the bottom row of H − 1 having a root at c = 1 2 . Using our definition, this can be written as h n , n + 1 ( c ) having a root at c = 1 2 . Using the formula for H − 1 we can write h n , n + 1 ( c ) as h n , n + 1 ( c ) = n + 1 � 2 � 2 n + 1 �� n + j �� n + j − 1 � ( − 1 ) n + j + 1 ( n + j ) c j − 1 n + j n + j n j = 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  25. Rearranging, simplifying, and shifting indicies gives us Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  26. Rearranging, simplifying, and shifting indicies gives us n � 2 n + 1 � � n �� n + k � h n , n + 1 ( c ) = ( − 1 ) n ( 2 n + 1 ) � ( − 1 ) k c k . n k k k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  27. Rearranging, simplifying, and shifting indicies gives us n � 2 n + 1 � � n �� n + k � h n , n + 1 ( c ) = ( − 1 ) n ( 2 n + 1 ) � ( − 1 ) k c k . n k k k = 0 This form is exactly what we need. The sum is our polynomial, and then we have a scaling factor outside. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  28. Rearranging, simplifying, and shifting indicies gives us n � 2 n + 1 � � n �� n + k � h n , n + 1 ( c ) = ( − 1 ) n ( 2 n + 1 ) � ( − 1 ) k c k . n k k k = 0 This form is exactly what we need. The sum is our polynomial, and then we have a scaling factor outside. All we need now is a definition to solve our problem. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  29. Definition The shifted Legendre polynomials, denoted ˜ P n ( x ) , are given by n � n �� n + k � P n ( x ) = ( − 1 ) n ˜ � ( − 1 ) k x k . k k k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  30. Definition The shifted Legendre polynomials, denoted ˜ P n ( x ) , are given by n � n �� n + k � P n ( x ) = ( − 1 ) n ˜ � ( − 1 ) k x k . k k k = 0 Looking back at our expresion for h n , n + 1 ( c ) , n � 2 n + 1 � � n �� n + k � h n , n + 1 ( c ) = ( − 1 ) n ( 2 n + 1 ) � ( − 1 ) k c k , n k k k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  31. Definition The shifted Legendre polynomials, denoted ˜ P n ( x ) , are given by n � n �� n + k � P n ( x ) = ( − 1 ) n ˜ � ( − 1 ) k x k . k k k = 0 Looking back at our expresion for h n , n + 1 ( c ) , n � 2 n + 1 � � n �� n + k � h n , n + 1 ( c ) = ( − 1 ) n ( 2 n + 1 ) � ( − 1 ) k c k , n k k k = 0 we can now see that h n , n + 1 ( c ) is just a multiple of ˜ P n ( c ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  32. The shifted Legendre polynomials are so named because they are, unsurprisingly, Legendre polynomials which have been shifted. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  33. The shifted Legendre polynomials are so named because they are, unsurprisingly, Legendre polynomials which have been shifted. The shift is given by sending x to 2 x − 1. That is, if we denote the Legendre polynomials by P n ( x ) , then P n ( 2 x − 1 ) = ˜ P n ( x ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  34. The shifted Legendre polynomials are so named because they are, unsurprisingly, Legendre polynomials which have been shifted. The shift is given by sending x to 2 x − 1. That is, if we denote the Legendre polynomials by P n ( x ) , then P n ( 2 x − 1 ) = ˜ P n ( x ) . The Legendre polynomials are known to have x = 0 as a root when their degree is odd. Therefore, the shifted Legendre polynomials must have a root at x = 1 2 when their degree is odd. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  35. So, h n , n + 1 ( c ) = a n and these are just multiples of the shifted Legendre polynomials. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  36. So, h n , n + 1 ( c ) = a n and these are just multiples of the shifted Legendre polynomials. The shifted Legendre polynomials have a root at 1 2 when their degree is odd. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  37. So, h n , n + 1 ( c ) = a n and these are just multiples of the shifted Legendre polynomials. The shifted Legendre polynomials have a root at 1 2 when their degree is odd. Therefore, if n is odd and c = 1 2 , then a n = 0. This ends up forcing f n ( x ) = f n − 1 ( x ) , thus answering our question. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  38. The appearance of Legendre polynomials is unsurprising since the original problem involves an inner product of polynomials. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  39. The appearance of Legendre polynomials is unsurprising since the original problem involves an inner product of polynomials. However, when I found this solution, It gave me another question. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  40. The appearance of Legendre polynomials is unsurprising since the original problem involves an inner product of polynomials. However, when I found this solution, It gave me another question. If h n , n + 1 ( c ) is always just a multiple of a shifted Legendre polynomial, what do other rows correspond to? Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  41. The appearance of Legendre polynomials is unsurprising since the original problem involves an inner product of polynomials. However, when I found this solution, It gave me another question. If h n , n + 1 ( c ) is always just a multiple of a shifted Legendre polynomial, what do other rows correspond to? That is, how does h n , 1 ( c ) change as we change n ? h n , 2 ( c ) ? etc. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  42. • Another Approach to the Problem and the Other Rows of H − 1 Until now, I have been using just basic calculus and matrix operations to answer these questions. There is however a better way. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  43. • Another Approach to the Problem and the Other Rows of H − 1 Until now, I have been using just basic calculus and matrix operations to answer these questions. There is however a better way. Theorem (Riesz Represention Theorem) If we have some finite dimensional vector space, V, and some linear functional φ on V, then there is a unique vector u ∈ V such that φ ( v ) = � v , u � for all v ∈ V. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  44. • Another Approach to the Problem and the Other Rows of H − 1 Until now, I have been using just basic calculus and matrix operations to answer these questions. There is however a better way. Theorem (Riesz Represention Theorem) If we have some finite dimensional vector space, V, and some linear functional φ on V, then there is a unique vector u ∈ V such that φ ( v ) = � v , u � for all v ∈ V. We can interpret our problem in terms of this theorem. The integral is an inner product, g ( x ) corresponds to v , f n ( x ) corresponds to u , and evaluation at c is a linear functional. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  45. This theorem has the consequence of allowing us to write n P k ( c )˜ ˜ P k ( x ) � f n ( x ) = � 1 ˜ P k ( x ) 2 dx k = 0 0 n � ( 2 k + 1 )˜ P k ( c )˜ = P k ( x ) k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  46. This theorem has the consequence of allowing us to write n P k ( c )˜ ˜ P k ( x ) � f n ( x ) = � 1 ˜ P k ( x ) 2 dx k = 0 0 n � ( 2 k + 1 )˜ P k ( c )˜ = P k ( x ) k = 0 It should be noted that this expression for f n ( x ) shows us that it is actually a familier concept in the study of orthogonal polynomials. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  47. This theorem has the consequence of allowing us to write n P k ( c )˜ ˜ P k ( x ) � f n ( x ) = � 1 ˜ P k ( x ) 2 dx k = 0 0 n � ( 2 k + 1 )˜ P k ( c )˜ = P k ( x ) k = 0 It should be noted that this expression for f n ( x ) shows us that it is actually a familier concept in the study of orthogonal polynomials. In this form f n ( x ) would be called the kernel of the shifted Legendre polynomials. Therefore what I am studying can be interpreted as looking at how the coefficients of this kernel change with n , and with c . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  48. Moving back to h n , i ( c ) , we can use the previous expression of f n ( x ) and the fact that n + 1 � h n , k ( c ) x k − 1 f n ( x ) = k = 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  49. Moving back to h n , i ( c ) , we can use the previous expression of f n ( x ) and the fact that n + 1 � h n , k ( c ) x k − 1 f n ( x ) = k = 1 To find that � k n �� k + i − 1 � ( 2 k + 1 )˜ � ( − 1 ) k + i − 1 h n , i ( c ) = P k ( c ) i − 1 i − 1 k = i − 1 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  50. Moving back to h n , i ( c ) , we can use the previous expression of f n ( x ) and the fact that n + 1 � h n , k ( c ) x k − 1 f n ( x ) = k = 1 To find that � k n �� k + i − 1 � ( 2 k + 1 )˜ � ( − 1 ) k + i − 1 h n , i ( c ) = P k ( c ) i − 1 i − 1 k = i − 1 Using this equation, I wanted to find a generating function for these polynomials. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  51. First let us focus on i = 1. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  52. First let us focus on i = 1. If i = 1 we have n � ( − 1 ) k ( 2 k + 1 )˜ h n , 1 ( c ) = P k ( c ) . k = 0 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  53. First let us focus on i = 1. If i = 1 we have n � ( − 1 ) k ( 2 k + 1 )˜ h n , 1 ( c ) = P k ( c ) . k = 0 Now we need to make use of a relationship between the shifted Legendre polynomials. ( n + 1 )˜ P n + 1 ( x ) = ( 2 n + 1 )( 2 x − 1 )˜ P n ( x ) − n ˜ P n − 1 ( x ) Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  54. First let us focus on i = 1. If i = 1 we have n � ( − 1 ) k ( 2 k + 1 )˜ h n , 1 ( c ) = P k ( c ) . k = 0 Now we need to make use of a relationship between the shifted Legendre polynomials. ( n + 1 )˜ P n + 1 ( x ) = ( 2 n + 1 )( 2 x − 1 )˜ P n ( x ) − n ˜ P n − 1 ( x ) Combining the two expressions, it can be shown that h n , 1 ( c ) = ( − 1 ) n ( n + 1 ) � � P n ( c ) + ˜ ˜ P n + 1 ( c ) 2 c Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  55. First let us focus on i = 1. If i = 1 we have n � ( − 1 ) k ( 2 k + 1 )˜ h n , 1 ( c ) = P k ( c ) . k = 0 Now we need to make use of a relationship between the shifted Legendre polynomials. ( n + 1 )˜ P n + 1 ( x ) = ( 2 n + 1 )( 2 x − 1 )˜ P n ( x ) − n ˜ P n − 1 ( x ) Combining the two expressions, it can be shown that h n , 1 ( c ) = ( − 1 ) n ( n + 1 ) � � P n ( c ) + ˜ ˜ P n + 1 ( c ) 2 c Using this we can find a generating function for h n , 1 ( c ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  56. Rearranging, multiplying by x n + 1 , and summing over n yields h n , 1 ( c ) x n + 1 ∞ ∞ 1 � P n ( c )( − x ) n + 1 + ˜ P n + 1 ( c )( − x ) n + 1 � � � ˜ = − n + 1 2 c n = 0 n = 0 � � ∞ ∞ = − 1 P n ( c )( − x ) n + P n ( c )( − x ) n − ˜ ˜ ˜ � � − x P 0 ( c ) 2 c n = 0 n = 0 � � ∞ = − 1 P n ( c ) x n − 1 ˜ � ( 1 − x ) 2 c n = 0 � � = − 1 1 − x 1 + 2 ( 2 c − 1 ) x + x 2 − 1 . � 2 c Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  57. Rearranging, multiplying by x n + 1 , and summing over n yields h n , 1 ( c ) x n + 1 ∞ ∞ 1 � P n ( c )( − x ) n + 1 + ˜ P n + 1 ( c )( − x ) n + 1 � � � ˜ = − n + 1 2 c n = 0 n = 0 � � ∞ ∞ = − 1 P n ( c )( − x ) n + P n ( c )( − x ) n − ˜ ˜ ˜ � � − x P 0 ( c ) 2 c n = 0 n = 0 � � ∞ = − 1 P n ( c ) x n − 1 ˜ � ( 1 − x ) 2 c n = 0 � � = − 1 1 − x 1 + 2 ( 2 c − 1 ) x + x 2 − 1 . � 2 c Now we take the derivative with respect to x of both sides which gives us the generating function. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  58. Let H 1 ( x ) be the generating function for h n , 1 ( c ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  59. Let H 1 ( x ) be the generating function for h n , 1 ( c ) . Then we have from the previous slide � � H 1 ( x ) = − 1 d 1 − x 1 + 2 ( 2 c − 1 ) x + x 2 − 1 � 2 c dx 1 + x = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  60. Now using our expression for H 1 ( x ) , along with � k n �� k + i − 1 � ( 2 k + 1 )˜ � ( − 1 ) k + i − 1 h n , i ( c ) = P k ( c ) i − 1 i − 1 k = i − 1 we can find an expression for the generating function of any h n , i ( c ) , denoted H i ( x ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  61. Sparing the details of the calculation, as it is more complicated but similar to the derivation of H 1 ( x ) , the final final result is given by � � ( − x ) i − 1 d 2 i − 2 x i − 1 ( 1 − x )( 1 + x ) H i ( x ) = ( 1 − x )(( i − 1 )!) 2 dx 2 i − 2 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  62. Sparing the details of the calculation, as it is more complicated but similar to the derivation of H 1 ( x ) , the final final result is given by � � ( − x ) i − 1 d 2 i − 2 x i − 1 ( 1 − x )( 1 + x ) H i ( x ) = ( 1 − x )(( i − 1 )!) 2 dx 2 i − 2 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 If we let j = i − 1 then this takes on a nicer form of � � d 2 j ( − x ) j x j ( 1 − x )( 1 + x ) H j + 1 ( x ) = ( 1 − x )( j !) 2 dx 2 j 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  63. Sparing the details of the calculation, as it is more complicated but similar to the derivation of H 1 ( x ) , the final final result is given by � � ( − x ) i − 1 d 2 i − 2 x i − 1 ( 1 − x )( 1 + x ) H i ( x ) = ( 1 − x )(( i − 1 )!) 2 dx 2 i − 2 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 If we let j = i − 1 then this takes on a nicer form of � � d 2 j ( − x ) j x j ( 1 − x )( 1 + x ) H j + 1 ( x ) = ( 1 − x )( j !) 2 dx 2 j 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 So we have accomplished our goal of finding the generating function for the polynomials h n , i ( c ) . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  64. Here are the first couple generating functions. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  65. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  66. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 2 ) x 2 − ( c 2 − c − 1 ) x + c − 1 ( c − 1 � � H 2 ( x ) = 12 x ( 1 + x ) 2 7 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  67. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 2 ) x 2 − ( c 2 − c − 1 ) x + c − 1 ( c − 1 � � H 2 ( x ) = 12 x ( 1 + x ) 2 7 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 H 3 ( x ) is a bit long so I will break it up a bit. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  68. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 2 ) x 2 − ( c 2 − c − 1 ) x + c − 1 ( c − 1 � � H 2 ( x ) = 12 x ( 1 + x ) 2 7 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 H 3 ( x ) is a bit long so I will break it up a bit. The denominator is the same as the others but with exponent 11 2 . Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  69. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 2 ) x 2 − ( c 2 − c − 1 ) x + c − 1 ( c − 1 � � H 2 ( x ) = 12 x ( 1 + x ) 2 7 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 H 3 ( x ) is a bit long so I will break it up a bit. The denominator is the same as the others but with exponent 11 2 . There is also the term 180 x 2 ( 1 + x ) which is also similar to the others. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  70. Here are the first couple generating functions. 1 + x H 1 ( x ) = 3 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 2 ) x 2 − ( c 2 − c − 1 ) x + c − 1 ( c − 1 � � H 2 ( x ) = 12 x ( 1 + x ) 2 7 ( 1 + 2 ( 2 c − 1 ) x + x 2 ) 2 H 3 ( x ) is a bit long so I will break it up a bit. The denominator is the same as the others but with exponent 11 2 . There is also the term 180 x 2 ( 1 + x ) which is also similar to the others. The part I want to show however, is the polynomial in the numerator. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

  71. For H 1 ( x ) the polynomial would just be 1. Scott Cameron A Linear Algebra Problem Related to Legendre Polynomials

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