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Chapter 6 Differential Equations

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Presentation on theme: "Chapter 6 Differential Equations"— Presentation transcript:

1 Chapter 6 Differential Equations
Chem Math 252 Chapter 6 Differential Equations

2 Differential Equations
Many problems in physical chemistry (eg. kinetics, dynamics, theoretical chemistry) require solution to a differential equation Many can not be solved analytically Deal only with first order ODE Higher order equations can be reduced to a system of 1st order DE

3 Differential Equations
Simplest form Can integrate analytically or numerically (using techniques of Chapter 4)

4 Differential Equations
General case Many simpler problems can be solved analytically Many involve ex However, in chemistry (physics & engineering) many problems have to be solved numerically (or approximately)

5 Picard Method Can not integrate exactly because integrand involves y
Approximate iteratively by using approximations for y Continue to iterate until a desire level of accuracy is obtained in y Often gives a power series solution

6 Picard Method – Example
Continue to iterate until a desire level of accuracy is obtained in y

7 Picard Method – Example 2

8 Euler Method Assume linear between 2 consecutive points
Between initial point and 1st (calculated) point User selects Dx Need to be careful - too big or too small can cause problems

9 Euler Method – Example

10 Taylor Method Based on Taylor expansion
Euler method is Taylor method of order 1 Use chain rule

11 Taylor Method – Example

12 Improved Euler (Heun’s) Method
Euler Method Use constant derivative between points i & i+1 calculated at xi Better to use average derivative across the interval yi+1 is not known Predict – Correct (can repeat)

13 Improved Euler Method – Example

14 Modified Euler Method Modified Euler Method
Use derivative halfway between points i & i+1

15 Modified Euler Method – Example

16 Runge-Kutta Methods Improved and Modified Euler Methods are special cases 2nd order Runge-Kutta 4th order Runge-Kutta Runge Kutta Runge-Kutta-Gill

17 Runge Methods

18 Kutta Methods

19 Runge-Kutta-Gill Methods

20 Systems of Equations All the previous methods can be applied to systems of differential equations Only illustrate the Runge method

21 Systems of Equations – Example 1

22 Systems of Equations – Example 2

23 Systems of Equations – Example 3

24 Systems of Equations – Example 4

25 Systems of Equations – Example 5

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