《MATLAB及其工程应用》第2讲.ppt

MATLAB Its Applications In Engineering 李清都 副教授 liqd@cqupt.edu.cn Lect. 2: Variables Arrays Arrays Vectors: 1 dimension Matrix: 2 or more dimensions A scalar is an array with only one row and one column. Variables Naming Rule must begin with a letter, followed by any combinations of letters, numbers, and the underscore character. C can begin with ‘_’ !!! Only the first 31 characters are significant. Special Variables i, j, pi, NaN, ans, eps Good Programming Practice Must using meaningful names Include a data dictionary in the header of the program Use lowercase letters to name a variable Use underscore as separator if the name is long Initialize the Array There are 3 common ways: Using assignment statement Read from a file From keyboard Initializing Variables in Assignment Statement Using assignment statement Var = expression Initializing with shortcut expression Var = first : incr : last Initializing with build-in functions Var = zeros(?) Var = ones(?) Initializing Variables from file MATLAB formatted file load xxx.mat save file_name var1, var2, var3… ASCII file load file_name.xxx -ascii Initializing Variables with Keyboard Input var = input(‘Enter an input value:’) Multi-dimensional Arrays Create a multi-dimensional array e.g. c is a 2x3x2 array c(:, :, 1) = [1 2 3; 4 5 6]; c(:, :, 2) = [7 8 9; 0 1 2]; MATLAB always allocates array elements in column major order. a(1, 1, 1) - a(2, 1, 1) - a(1, 2, 1) - a(2, 2, 1) - a(1, 3, 1)… a(10) = 1 Subarray Select and use subsets of a array c = [1 2 3; 4 5 6]; a = c(1, [ 2 3]) b = c([1 2], [ 2 3]) The end function c(1, 2:end) Assignment to subarray c(1, [ 2 3]) = [12 13] Assigning a scalar to a subarray