Ví dụ, đối tượng của lớp Employee có thể là John Doe, Fred Smith, và các nhân viên khác của công ty. Lớp nhân viên đưa ra những thông tin và hành vi của các đối tượng nhân viên sẽ có. Để thiết lập các lớp học trở lại hoạt động: 1. Kích chuột phải vào hoạt động trong trình duyệt. 2. Chọn Đặc điểm kỹ thuật Open từ menu chuột phải. 3. | CHAPTER 9 Transforms 221 J laplace t s ans 120 s 6 From this we deduce the well-known formula t tn SẾ Now let s look at the Laplace transform of some common functions seen in science and engineering. First consider the decaying exponential laplace exp -b t ans 1 s b The Laplace transforms of the sin and cos functions are laplace cos w t ans s sA2 wA2 laplace sin w t ans w sA2 wA2 We can also calculate the Laplace transform of the hyperbolic cosine function laplace cosh b t ans s sA2-bA2 The Laplace transform is linear. That is l af t bg t al f t bl g t í 222 MATLAB Demystified Let s verify this with MATLAB. Let f 5 exp -2 t We find that the Laplace transform is laplace f ans 5 s 1 s 2 The Inverse Laplace Transform Computing inverse Laplace transforms is something sure to generate a lot of headaches among readers who are taking say a circuits analysis class. This process is often very tedious and filled with lots of difficult algebra. But with MATLAB our problems are solved. We can compute the inverse Laplace transform by typing ilaplace saving us from having to do partial fraction decompositions and other nasty tricks. First let s get familiar with computing inverse Laplace transforms by looking at some simple examples. First consider a simple power function ilaplace 1 s 3 ans 1 2 tA2 Or with this one we get an exponential ilaplace 2 w s ans 2 exp -w t And finally an example involving a trig function ilaplace s s 2 4 ans cos 2 t CHAPTER 9 Transforms 223 J Of course most problems you come across in applications don t result in inverse Laplace transforms where you can just spot the answer like in these examples. This is where MATLAB is really useful. For instance what is the inverse Laplace transform of 5 3s F s 2 5 Let s enter it into MATLAB F 5-3 s 2 5 s Computing the inverse Laplace transform we find a Dirac delta function or unit impulse function for engineers ilaplace F ans -3 5 dirac t 31 25 exp -2 5 t Here is a more complicated example. What do you think the .
