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Page 1 ?= + - ? ? ? + -+ + ? ? ? dy dx h y p y pp y 12 1 2 36 2 3 0 2 0 2 3 0 ?? ? () ! () ! ? ? ? ? ? ? ? dy dx at x = x 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy … ( \ At i = x 0 ; p = 0) And dy dx d dx dy dx d dp dy dx dp dx h 2 2 1 = ? ? ? ? ? ? = ? ? ? ? ? ? = ?? ? 2 0 3 0 2 4 0 66 3 12 36 22 4 1 y p y pp y h + - + -+ ? ? ? ? ? ? !! dy dx h y p y pp y 2 2 2 0 3 0 2 4 0 16 6 3 12 36 22 1 2 ? ? ? ? ? ? =? + - ?+ -+ ? ? ? ? ? ? ? !! dy dx xx 2 2 0 ? ? ? ? ? ? = at =? -? +? -? + ? ? ? ? ? ? 111 12 5 6 2 2 0 3 0 4 0 5 0 h yy yy \ By using Newton’ s forward interpolation formula, the first and second derivatives of y = f (x) at x = x 0 are given by dy dx xx ? ? ? ? ? ? = 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy y… and dy dx h yy yy xx 2 22 2 0 3 0 4 0 5 0 0 111 12 5 6 ? ? ? ? ? ? =? -? +? -? + ? ? ? ? ? ? = … 2. Derivatives using newton’s backward difference interpolation formula: We know that the Newton’s backward difference interpolation formula is y = y n + p? y n + pp () ! +1 2 ? 2 y n + pp p ()() ! ++ 12 3 + ? 3 y n … Differentiating on both sides wrt p, dy dx y p y pp y nn n =? + + ?+ ++ ?+ 21 2 36 2 3 2 2 3 ! As p xx h dp dx h n = - = 1 Chapter 06.indd 131 5/31/2017 10:59:42 AM Page 2 ?= + - ? ? ? + -+ + ? ? ? dy dx h y p y pp y 12 1 2 36 2 3 0 2 0 2 3 0 ?? ? () ! () ! ? ? ? ? ? ? ? dy dx at x = x 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy … ( \ At i = x 0 ; p = 0) And dy dx d dx dy dx d dp dy dx dp dx h 2 2 1 = ? ? ? ? ? ? = ? ? ? ? ? ? = ?? ? 2 0 3 0 2 4 0 66 3 12 36 22 4 1 y p y pp y h + - + -+ ? ? ? ? ? ? !! dy dx h y p y pp y 2 2 2 0 3 0 2 4 0 16 6 3 12 36 22 1 2 ? ? ? ? ? ? =? + - ?+ -+ ? ? ? ? ? ? ? !! dy dx xx 2 2 0 ? ? ? ? ? ? = at =? -? +? -? + ? ? ? ? ? ? 111 12 5 6 2 2 0 3 0 4 0 5 0 h yy yy \ By using Newton’ s forward interpolation formula, the first and second derivatives of y = f (x) at x = x 0 are given by dy dx xx ? ? ? ? ? ? = 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy y… and dy dx h yy yy xx 2 22 2 0 3 0 4 0 5 0 0 111 12 5 6 ? ? ? ? ? ? =? -? +? -? + ? ? ? ? ? ? = … 2. Derivatives using newton’s backward difference interpolation formula: We know that the Newton’s backward difference interpolation formula is y = y n + p? y n + pp () ! +1 2 ? 2 y n + pp p ()() ! ++ 12 3 + ? 3 y n … Differentiating on both sides wrt p, dy dx y p y pp y nn n =? + + ?+ ++ ?+ 21 2 36 2 3 2 2 3 ! As p xx h dp dx h n = - = 1 Chapter 06.indd 131 5/31/2017 10:59:42 AM ?= dy dx dy dp dp dx =? + + ?+ ++ ?+ ? ? ? ? ? ? y p y pp y h nn n 21 2 36 2 3 1 2 2 3 !! ?= ?+ + ?+ ++ ? ? ? ?+ ? ? ? dy dx h y p y pp y nn n 12 1 2 36 2 3 2 2 3 !! dy dx xx n ? ? ? ? ? ? = =? +? +? +? +? + ? ? ? ? ? ? 11 2 1 3 1 4 1 5 23 45 h yy yy y nn nn n ... ( \ At x = x n ; p = 0) And dy dx d dx dy dx d dp dy dx dp dx 2 2 = ? ? ? ? ? ? = ? ? ? ? ? ? =? + + ?+ ++ ? ? ? ?+ ? ? ? 16 6 3 12 36 22 4 1 23 2 4 h y p y pp y h nn n !! ?= dy dx h 2 22 1 ?+ + ?+ ++ ?+ ? ? ? ? ? ? 23 2 4 66 3 12 36 22 4 y p y pp y nn n !! ? ? ? ? ? ? ? =? +? +? +? ? ? ? ? ? ? = dy dx h yy yy xx nn nn n 2 22 23 45 111 12 5 6 \ By using Newton’s backward difference interpolation formula, the first and second derivatives of y = f (x) at x = x n are given by dy dx xx n ? ? ? ? ? ? = =? +? +? +? +? + ? ? ? ? ? ? 11 2 1 3 1 4 1 5 23 45 h yy yy y nn nn n and dy dx xx n 2 2 ? ? ? ? ? ? = =? +? +? +? + ? ? ? ? ? ? 111 12 5 6 2 23 45 h yy yy nn nn Example Using the values of a function y = f (x) given in the following table, find the first two derivatives of f (x) at x = 7. x 2 3 4 5 6 7 y = f(x) 4 8 15 27 36 42 Solution As we have to find the first two derivatives of y = f (x) at x = 7, (end point of the given data), we use the derivatives’ formulae obtained from Newton’s backward interpolation formula. The backward difference table for the given data is X y = f(x) Dy D 2 y D 3 y D 4 y D 5 y 2 3 4 5 6 7 4 8 15 27 36 42 4 7 12 9 6 3 5 -3 -3 -2 -8 0 6 8 2 By Newton’s backward interpolation formula, we have dy dx xx n ? ? ? ? ? ? ==7 =? +? +? +? +? ? ? ? ? ? ? 11 2 1 3 1 5 23 45 h yy yy y nn nn n =+ ×- +× +× +× ? ? ? ? ? ? == 1 1 6 1 2 3 1 3 0 1 4 8 1 5 2 69 10 69 () . And dy dx xx n 2 2 7 ? ? ? ? ? ? == =? +? ++?+ ? ? ? ? ? ? ? 111 12 5 6 2 23 45 h yy yy nn nn =- ++ ×+ × ? ? ? ? ? ? = 1 1 30 11 12 8 5 6 26 2 . Example Find the first derivative at x = 6 for a function y = f (x) with the following data. x 5 7 10 11 13 y = f(x) 100 294 900 1210 2028 Solution As the given values of x are not equally spaced, to find the first derivative of f(x), we will make use of the Newton’s divided difference interpolation formula, which is given by y = f(x) = f(x 0 ) + (x - x 0 ) [x 0 , x 1 ] + (x - x 0 )(x - x 1 ) [x 0 , x 1 , x 2 ] + (x - x 0 )(x - x 1 )(x - x 2 ) [x 0 , x 1 , x 2 x 3 ] + (x - x 0 )(x - x 1 )(x - x 2 ) (x - x 3 )][x 0 , x 1 , x 2 , x 3 , x 4 ] + … (1) The divided differences of various orders for the given data can be represented as shown below. Chapter 06.indd 132 5/31/2017 10:59:45 AM Page 3 ?= + - ? ? ? + -+ + ? ? ? dy dx h y p y pp y 12 1 2 36 2 3 0 2 0 2 3 0 ?? ? () ! () ! ? ? ? ? ? ? ? dy dx at x = x 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy … ( \ At i = x 0 ; p = 0) And dy dx d dx dy dx d dp dy dx dp dx h 2 2 1 = ? ? ? ? ? ? = ? ? ? ? ? ? = ?? ? 2 0 3 0 2 4 0 66 3 12 36 22 4 1 y p y pp y h + - + -+ ? ? ? ? ? ? !! dy dx h y p y pp y 2 2 2 0 3 0 2 4 0 16 6 3 12 36 22 1 2 ? ? ? ? ? ? =? + - ?+ -+ ? ? ? ? ? ? ? !! dy dx xx 2 2 0 ? ? ? ? ? ? = at =? -? +? -? + ? ? ? ? ? ? 111 12 5 6 2 2 0 3 0 4 0 5 0 h yy yy \ By using Newton’ s forward interpolation formula, the first and second derivatives of y = f (x) at x = x 0 are given by dy dx xx ? ? ? ? ? ? = 0 =? -? +? -? +? ? ? ? ? ? ? 11 2 1 3 1 4 1 5 0 2 0 3 0 4 0 5 0 h yy yy y… and dy dx h yy yy xx 2 22 2 0 3 0 4 0 5 0 0 111 12 5 6 ? ? ? ? ? ? =? -? +? -? + ? ? ? ? ? ? = … 2. Derivatives using newton’s backward difference interpolation formula: We know that the Newton’s backward difference interpolation formula is y = y n + p? y n + pp () ! +1 2 ? 2 y n + pp p ()() ! ++ 12 3 + ? 3 y n … Differentiating on both sides wrt p, dy dx y p y pp y nn n =? + + ?+ ++ ?+ 21 2 36 2 3 2 2 3 ! As p xx h dp dx h n = - = 1 Chapter 06.indd 131 5/31/2017 10:59:42 AM ?= dy dx dy dp dp dx =? + + ?+ ++ ?+ ? ? ? ? ? ? y p y pp y h nn n 21 2 36 2 3 1 2 2 3 !! ?= ?+ + ?+ ++ ? ? ? ?+ ? ? ? dy dx h y p y pp y nn n 12 1 2 36 2 3 2 2 3 !! dy dx xx n ? ? ? ? ? ? = =? +? +? +? +? + ? ? ? ? ? ? 11 2 1 3 1 4 1 5 23 45 h yy yy y nn nn n ... ( \ At x = x n ; p = 0) And dy dx d dx dy dx d dp dy dx dp dx 2 2 = ? ? ? ? ? ? = ? ? ? ? ? ? =? + + ?+ ++ ? ? ? ?+ ? ? ? 16 6 3 12 36 22 4 1 23 2 4 h y p y pp y h nn n !! ?= dy dx h 2 22 1 ?+ + ?+ ++ ?+ ? ? ? ? ? ? 23 2 4 66 3 12 36 22 4 y p y pp y nn n !! ? ? ? ? ? ? ? =? +? +? +? ? ? ? ? ? ? = dy dx h yy yy xx nn nn n 2 22 23 45 111 12 5 6 \ By using Newton’s backward difference interpolation formula, the first and second derivatives of y = f (x) at x = x n are given by dy dx xx n ? ? ? ? ? ? = =? +? +? +? +? + ? ? ? ? ? ? 11 2 1 3 1 4 1 5 23 45 h yy yy y nn nn n and dy dx xx n 2 2 ? ? ? ? ? ? = =? +? +? +? + ? ? ? ? ? ? 111 12 5 6 2 23 45 h yy yy nn nn Example Using the values of a function y = f (x) given in the following table, find the first two derivatives of f (x) at x = 7. x 2 3 4 5 6 7 y = f(x) 4 8 15 27 36 42 Solution As we have to find the first two derivatives of y = f (x) at x = 7, (end point of the given data), we use the derivatives’ formulae obtained from Newton’s backward interpolation formula. The backward difference table for the given data is X y = f(x) Dy D 2 y D 3 y D 4 y D 5 y 2 3 4 5 6 7 4 8 15 27 36 42 4 7 12 9 6 3 5 -3 -3 -2 -8 0 6 8 2 By Newton’s backward interpolation formula, we have dy dx xx n ? ? ? ? ? ? ==7 =? +? +? +? +? ? ? ? ? ? ? 11 2 1 3 1 5 23 45 h yy yy y nn nn n =+ ×- +× +× +× ? ? ? ? ? ? == 1 1 6 1 2 3 1 3 0 1 4 8 1 5 2 69 10 69 () . And dy dx xx n 2 2 7 ? ? ? ? ? ? == =? +? ++?+ ? ? ? ? ? ? ? 111 12 5 6 2 23 45 h yy yy nn nn =- ++ ×+ × ? ? ? ? ? ? = 1 1 30 11 12 8 5 6 26 2 . Example Find the first derivative at x = 6 for a function y = f (x) with the following data. x 5 7 10 11 13 y = f(x) 100 294 900 1210 2028 Solution As the given values of x are not equally spaced, to find the first derivative of f(x), we will make use of the Newton’s divided difference interpolation formula, which is given by y = f(x) = f(x 0 ) + (x - x 0 ) [x 0 , x 1 ] + (x - x 0 )(x - x 1 ) [x 0 , x 1 , x 2 ] + (x - x 0 )(x - x 1 )(x - x 2 ) [x 0 , x 1 , x 2 x 3 ] + (x - x 0 )(x - x 1 )(x - x 2 ) (x - x 3 )][x 0 , x 1 , x 2 , x 3 , x 4 ] + … (1) The divided differences of various orders for the given data can be represented as shown below. Chapter 06.indd 132 5/31/2017 10:59:45 AM x y = f(x) First divided differences Second divided differences Third divided differences Fourth divided differences 5 7 10 11 13 100 294 900 1,210 2,028 294 100 75 97 - - = 900 294 10 7 202 - - = 1210 900 11 10 310 - - = 2028 1210 13 11 409 - - = 202 97 10 5 21 - - = 310 202 11 7 27 - - = 409 310 13 10 33 - - = 27 21 11 5 1 - - = 33 27 13 7 1 - - = 11 13 5 0 - - = Substituting these in Eq. (1), we get y = f(x) = 100 + (x - 5) × 97 + (x - 5)(x - 7) 21 + (x - 5) (x - 7)(x - 10) × 1 + (x - 5)(x - 7)(x - 10)(x - 11) × 0 \ f (x) = 100 + 97(x - 5) + 21(x 2 - 12x + 35) + (x 3 - 22x 2 + 155x - 350) ?= dy dx 97 + 21(2x - 12) + (3x 2 - 44x + 155) ? ? ? ? ? ? ? = dy dx x 6 = 97 + 21(2 × 6 - 12) + (3 × 6 2 - 44 × 6 +155) = 97 + 0 + (- 1) = 96. 0 0 + ? ? ? y n y nn 0 0 23 + + - ? ? ( Chapter 06.indd 133 5/31/2017 10:59:48 AMRead More
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