Hai âm mưu lệnh cùng với sinc1 (t, D) và sinc1 (t) sản lượng trong hai đồ thị đẹp, tương ứng, như mô tả trong hình. . Điều quan trọng là cần lưu ý rằng sinc1 () không làm phiền chúng tôi và hoạt động tốt mà không có đầu vào đối số thứ hai D. | 42 MATLAB USAGE AND COMPUTATIONAL ERRORS Figure The graphs of a sinc function defined by sinc1 . D bl -2 b2 2 t b1 0 200 200 b2 - b1 plot t sinc1 t D axis b1 b2 hold on plot t sinc1 t k The two plotting commands coupled with sinc1 t D and sinc1 t yield the two beautiful graphs respectively as depicted in Fig. . It is important to note that sinc1 doesn t bother us and works fine without the second input argument D. We owe the second line in the function sinc1 for the nice errorhandling service if nargin 2 D 1 end This line takes care of the case where the number of input arguments nargin is less than 2 by assuming that the second input argument is D 1 by default. This programming technique is the key to making the MATLAB functions adaptive to different number type of input arguments which is very useful for breathing the user-convenience into the MATLAB functions. To appreciate its role we remove the second line from the M-file defining sinc1 and then type the same statement in the Command window trying to use sinc1 without the second input argument. plot t sinc1 t k Input argument D is undefined. Error in C MATLAB6p5 nma On line 4 x sin pi t D . pi t D This time we get a serious red error message with no graphic result. It is implied that the MATLAB function without the appropriate error-handling parts no longer allows the user s default or carelessness. Now consider the third line in sinc1 which is another error-handling statement. t find t 0 eps TOWARD GOOD PROGRAM 43 or equivalently for i 1 length t if t i 0 t i eps end end This statement changes every zero element in the t vector into eps . What is the real purpose of this statement It is actually to remove the possibility of division-by-zero in the next statement which is a mathematical expression having t in the denominator. x sin pi t D . pi t D To appreciate the role of the third line in sinc1 we remove it from the M-file defining sinc1 and type the following .