matlab programming (flow control)

8/12/2019 MATLAB PROGRAMMING (FLOW CONTROL)

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ML102

MATLAB PROGRAMMING

Flow Control

MATLAB has several flow control constructs but the basic flow control or

command word for solving mathematical and engineering problems are:

if

switch and case

for

while

continue

break

try-catch

return

if: The if statement evaluates a conditional expression and executes a group

of statements when the expression is true. The optional elseif and else

keywords provide for the execution of the alternate groups of statements. An

end keyword, which matches the if, terminates the last group of statements.

Examples:

1. x=input('what is the value of x:');

y = abs(x)

ifx >= 0

y = x;

else

y = -x;

end

Note: The second line of this M-file states that the function has a single input x

and a single output y. If the input x is nonnegative, the ifstatement is

determined by MATLAB to be true. Then the command between the ifand

the elsestatements is executed to set y equal to x, while MATLAB skips the

command between the else and end statements. However, if x is negative,


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then MATLAB skips to the else statement and executes the succeeding

command, setting y equal to -x.

2. x=input('what is the value of x:');

y = sign(x)ifx > 0

y = 1;

elseifx == 0

y = 0;

else

y = -1;

end

Note:The elseifstatement is useful if there are more than two alternatives

and they can be distinguished by a sequence of true/false tests.In example 2, if the input x is positive, then the output y is set to 1 and all

commands from the elseif statement to the end statement are skipped. (In

particular, the test in the elseif statement is not performed.) If x is not

positive, then MATLAB skips to the elseif statement and tests to see if x

equals 0. If so, y is set to 0; otherwise y is set to -1. Notice that MATLAB

requires a double equal sign == to test for equality in logic statement; a single

equal sign is reserved for the assignment of values to variables.

Exercises:

i)

Write a program to input students score and display the grade. ii) Write a program that will read the account of a customer and

compute his interest.

Note: The interest rate is 9% for balance that is less than 5,000. The

interest is 12% for balance greater or equal to 5,000 and less than

10,000. The interest is 15% for balance greater than or equal to

10,000.

for: Thefor statement repeats a group of statements a fixed, predetermined

number of times. A matching enddelineates the statements.

Examples:

1)for n=(1:5);

X=2.^n


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end

2)s=0;

for n= (1:3);

x=2.^n

s=s+x;end

Exercises:

1)Write a program that will generate first five terms of the sequence

X(n)=(a^n)/n! and find its sum. (a=2).

2)Write a program to find the sum of the first five terms of the series 1,

1/(2^2), 1/(3^2), 1/(4^2),

Solutions:

Question 1 can solve via two methods, namely, vectorization method and the

loop method. Loop method makes use offor statement but vectorization doesnot.

Loop method: loop method:

for N=1:5; S=0;

X=2^N/factorial(N) for N=1:5;

S=0 X=2^N/factorial(N)

for N=1:5; S=S+X

S=S+ X=2^N/factorial(N) end

end

end

Vectorization method:

N=[1:5];

X=(2.^N)./factorial(N)

S=sum(X)

NOTE:for statement does not recognize element by element operations. For

element by element operations, use dot (.) or else it will see it as a matrix. This

means that for scalar multiplication dot (.) is used.

matlab programming (flow control)

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