Bạn cũng có thể cho thấy tầm nhìn của mỗi thuộc tính và hoạt động, loại dữ liệu thuộc tính mỗi, và chữ ký của từng hoạt động trên các sơ đồ. Chúng tôi sẽ thảo luận về các tùy chọn này trong chương kế tiếp. Lớp nhân viên này sẽ trở thành một khuôn mẫu cho các đối tượng nhân viên. Một đối tượng là một thể hiện của một lớp. | Figure 7-6 In the second case examined in Example 7-1 we get a nice plot showing the response lagging the forcing function with both functions having the same general shape Solving Second Order Equations Now let s see how to solve second order equations numerically. The trick used here is to break the equation down into a system of two equations. So first let s see how to solve a system of equations. EXAMPLE 7-2 Solve the system dx _ 2 dy _ dt x y dt - x - xy with initial conditions x 0 0 y 0 1. Plot both functions and generate a phase plot. SOLUTION 7-2 First we create a function like before that will implement the right-hand side of the differential equation. This time of course we have a system so need a 2 X 1 column vector. The function looks like this function xdot eqx t x allocate array to store data CHAPTER 7 Numerical Solution of ODEs 189 J xdot zeros 2 1 xdot 1 -x 1 A2 x 2 xdot 2 -x 1 - x 1 x 2 So far so good pretty simple. Now let s use ode45 to generate a solution with the given initial conditions t x ode45 eqx 0 10 0 1 Now let s generate a plot. We access the first function with x 1 and the second by writing x 2 . The plot command is plot t x 1 t x 2 -- xlabel t axis 0 10 The plot of the two functions is shown in Figure 7-7. Now let s generate the phase plot. The command is plot x 1 x 2 The phase plot is shown in Figure 7-8. Now that we know how to solve a system we can use ode45 to solve a second order equation. Figure 7-7 The functions x solid line and y dashed line that solve the system in Example 7-2 190 MATLAB Demystified Figure 7-8 The phase portrait for the system solved in Example 7-2 EXAMPLE 7-3 Find a solution of y 16y sin when y 0 y 0 0. SOLUTION 7-3 We can change this into a system of first order equations. First we set 1 y 2 y Hence 1 y 2 2 y sin - 16x1 Now we create a function to implement this system function xdot eqx2 t x allocate array to store data xdot zeros 2 1 xdot 1 x 2 xdot 2 sin t -16 x 1
