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# ch03 - Attia John Okyere “Control Statements.”...

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Unformatted text preview: Attia, John Okyere. “Control Statements .” Electronics and Circuit Analysis using MATLAB. Ed. John Okyere Attia Boca Raton: CRC Press LLC, 1999 © 1999 by CRC PRESS LLC CHAPTER THREE CONTROL STATEMENTS 3.1 FOR LOOPS “ FOR ” loops allow a statement or group of statements to be repeated a fixed number of times. The general form of a for loop is for index = expression statement group X end The expression is a matrix and the statement group X is repeated as many times as the number of elements in the columns of the expression matrix. The index takes on the elemental values in the matrix expression. Usually, the ex- pression is something like m:n or m:i:n where m is the beginning value, n the ending value, and i is the increment. Suppose we would like to find the squares of all the integers starting from 1 to 100. We could use the following statements to solve the problem: sum = 0; for i = 1:100 sum = sum + i^2; end sum For loops can be nested, and it is recommended that the loop be indented for readability. Suppose we want to fill 10-by-20 matrix, b, with an element value equal to unity, the following statements can be used to perform the operation. % n = 10; % number of rows m = 20; % number of columns for i = 1:n for j = 1:m b(i,j) = 1; % semicolon suppresses printing in the loop end end © 1999 CRC Press LLC © 1999 CRC Press LLC b % display the result % It is important to note that each for statement group must end with the word end . The following program illustrates the use of a for loop. Example 3.1 The horizontal displacement x t ( ) and vertical displacement y t ( ) are given with respect to time, t, as x t t y t t ( ) ( ) sin( ) = = 2 For t = 0 to 10 ms, determine the values of x t ( ) and y t ( ) . Use the values to plot x t ( ) versus y t ( ) . Solution : MATLAB Script % for i= 0:10 x(i+1) = 2*i; y(i+1) = 2*sin(i); end plot(x,y) Figure 3.1 shows the plots of x t ( ) and y t ( ) . © 1999 CRC Press LLC © 1999 CRC Press LLC Figure 3.1 Plot of x versus y. 3.2 IF STATEMENTS IF statements use relational or logical operations to determine what steps to perform in the solution of a problem. The relational operators in MATLAB for comparing two matrices of equal size are shown in Table 3.1 . Table 3.1 Relational Operators RELATIONAL OPERATOR MEANING < less than <= less than or equal > greater than >= greater than or equal == equal ~= not equal © 1999 CRC Press LLC © 1999 CRC Press LLC When any of the above relational operators are used, a comparison is done be- tween the pairs of corresponding elements. The result is a matrix of ones and zeros, with one representing TRUE and zero FALSE. For example, if a = [1 2 3 3 3 6]; b = [1 2 3 4 5 6]; a == b The answer obtained is ans = 1 1 1 0 0 1 The 1s indicate the elements in vectors a and b that are the same and 0s are the ones that are different....
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ch03 - Attia John Okyere “Control Statements.”...

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