Example Improved Eulers Method Error Order of Error Improved Eulers Method

# Example improved eulers method error order of error

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Example Improved Euler’s Method Error Order of Error Improved Euler’s Method Error Improved Euler’s Method Error Showed earlier that Euler’s method had a local truncation error of O ( h 2 ) with global error being O ( h ) Similar Taylor expansions (in two variables) give the local truncation error for the Improved Euler’s method as O ( h 3 ) For Improved Euler’s method , the global truncation error is O ( h 2 ) From a practical perspective, these results imply: With Euler’s method , the reduction of the stepsize by a factor of 0.1 gains one digit of accuracy With Improved Euler’s method , the reduction of the stepsize by a factor of 0.1 gains two digits of accuracy This is a significant improvement at only the cost of one additional function evaluation per step Joseph M. Mahaffy, h [email protected] i Lecture Notes – Numerical Methods for Different — (34/39) Introduction Euler’s Method Improved Euler’s Method Improved Euler’s Method - Algorithm Example Improved Euler’s Method Error Order of Error Numerical Example 1 Numerical Example: Consider the IVP dy dt = 2 e - 0 . 1 t - sin( y ) , y (0) = 3 , which has no exact solution, so must solve numerically Solve this problem with Euler’s method and Improved Euler’s method Show differences with different stepsizes for t [0 , 5] Show the order of convergence by halving the stepsize twice Graph the solution and compare to solution from ode23 in MatLab, closely approximating the exact solution Joseph M. Mahaffy, h [email protected] i Lecture Notes – Numerical Methods for Differential Equations — (35/39) Introduction Euler’s Method Improved Euler’s Method Improved Euler’s Method - Algorithm Example Improved Euler’s Method Error Order of Error Numerical Example 2 Numerical Solution for dy dt = 2 e - 0 . 1 t - sin( y ) , y (0) = 3 Used MatLab’s ode45 to obtain an accurate numerical solution to compare Euler’s method and Improved Euler’s method with stepsizes h = 0 . 2, h = 0 . 1, and h = 0 . 05 “Actual” Euler Im Eul Euler Im Eul Euler Im Eul t n h = 0 . 2 h = 0 . 2 h = 0 . 1 h = 0 . 1 h = 0 . 05 h = 0 . 05 0 3 3 3 3 3 3 3 1 5.5415 5.4455 5.5206 5.4981 5.5361 5.5209 5.5401 2 7.1032 7.1718 7.0881 7.1368 7.0995 7.1199 7.1023 3 7.753 7.836 7.743 7.7939 7.7505 7.7734 7.7524 4 8.1774 8.2818 8.167 8.2288 8.1748 8.2029 8.1768 5 8.5941 8.7558 8.5774 8.6737 8.5899 8.6336 8.5931 1 . 88% - 0 . 194% 0 . 926% - 0 . 0489% 0 . 460% - 0 . 0116% Last row shows percent error between the different approximations and the accurate solution Joseph M. Mahaffy, h jmahaffy[email protected] i Lecture Notes – Numerical Methods for Different — (36/39)

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Introduction Euler’s Method Improved Euler’s Method Improved Euler’s Method - Algorithm Example Improved Euler’s Method Error Order of Error Numerical Example 3 Error of Numerical Solutions Observe that the Improved Euler’s method with stepsize h = 0 . 2 is more accurate at t = 5 than Euler’s method with stepsize h = 0 . 05 With Euler’s method the error cuts in half with halving of the stepsize With the Improved Euler’s method the errors cuts in quarter with halving of the stepsize Joseph M. Mahaffy, h [email protected] i Lecture Notes – Numerical Methods for Differential Equations — (37/39) Introduction Euler’s Method Improved Euler’s Method Improved Euler’s Method - Algorithm Example
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