Đây là một đầu mối rằng câu trả lời ở trên là một chuỗi (bao gồm một trong những nhân vật), không phải là một số điểm nổi. Typing f (5) sẽ mang lại - và f (-1) sẽ tạo ra một thông báo lỗi. Bạn đã học được cách để xác định các chức năng của riêng bạn, | 81 f f x erf x n 8 c 0. 8. Plot the following surfaces a z sin x sin y for 3n x 3n and 3n y 3n b z x2 y2 cos x2 y2 for 1 x 1 and 1 y 1. 9. Create a 17-frame movie whose frames show filled red circles of radius 1 2 centered at the points 4cos jn 8 4sm j n 8 j 0 1 . 16. Make sure that all the circles are drawn on the same set of axes and that they look like circles not ellipses. 10. In this problem we use the backslash operator or left-matrix-divide operator introduced in the section Solving Linear Systems of Chapter 4. a Use the backslash operator to solve the system of linear equations in Problem 3 of Practice Set A. b Now try the same method on Problem 4 of Practice Set A. MATLAB finds one but not all answer s . Can you explain why If not see Problem 11 below as well as part d of this problem c Next try the method on this problem w 3x 2y 4z 1 2w 3x 4y z 1 4w 3x y 2z 1 2w 3x 4y z 1. Check your answer by matrix multiplication. d Finally try the matrix division method on ax by u cx dy v. Don t forget to declare the variables to be symbolic. Your answer should involve a fraction and so will be valid only when its denominator is nonzero. Evaluate det on the coefficient matrix of the system. Compare this with the denominator. 11. We deal in this problem with 3 X 3 matrices although the concepts are valid in any dimension. a Consider the rows of a square matrix A. They are vectors in 3-space and so span a subspace of dimension 3 2 1 or possibly 0 if all the entries of A are zero . That number is called the rank of A. The MATLAB command rank computes the rank of a matrix. Try it on the four coefficient matrices in each of the parts of Problem 10. Comment on MATLAB s answer for the fourth one. 82 Practice Set B. Calculus Graphics and Linear Algebra b An n X n matrix is non-singular if its rank is n. Which of the four you computed in part a are non-singular c Another measure of non-singularity is given by the determinant - a fundamental result in linear algebra is that a .
