Module (2) Loops and Condition in MATLAB and Excel

Module (2) Loops and Condition in MATLAB and Excel

 

1.     Logical and Relational Operations in MATLAB

Suppose that you have two arrays A and B, and you want to test the relationship between them, So you can check this by using some logical operators such as (>, <,=, ~,&,|). If the Condition is matched, it will (1) or give (0).

Let's test the following commands:

<	Smaller Than
>	Greater than
=	Equal
~	Not equal
&	And
|	OR

 

> A=[1 2 3 4 5]

A =1.00          2.00          3.00          4.00          5.00

>> B=[2 1 5 4 -1]

B = 2.00          1.00          5.00          4.00         -1.00

>> A>B

ans = 1×5 logical array

0   1   0   0   1

>> A>=B

ans =1×5 logical array

0   1   0   1   1

>> A<B

ans = 1×5 logical array

1   0   1   0   0

>> A==B

ans =1×5 logical array

0   0   0   1   0

>> A~=B

ans =1×5 logical array

1   1   1   0   1

 

 

2.     Creating a script in MATLAB using M.Files

You can write a series of statements in M.file to run all at once by CTR+N or New Script.

M files can be a script file or function file.

In a script file, a series of MATLAB commands can be executed at once either by typing the saved file name in the command window or by select Run.

You can perform the logical and relational operations in MATLAB using M.Files. Let us try it. In a new script file, write the following codes and save it as Untitled, then; in the command window, type Untitled or select Run

Example

Create a script Insert students grades and find who got A

Function (find)

It is used to locate the nonzero elements in a vector or a matrix.

Example 1

Create a script file where students' grades can be inserted in a vector.

Show the students' grade who got (A) (i.e. >=90) and their location in the vector.

Example 2

Create a script file in which you can insert car speeds and catches those speed >=80.

Example 3

Create M file to list values of X and Y in a proper table and plot them

__________

 

Function (tic&toc)

tic and toc are used to calculate the elapsed time between them

Example

Create M file to Program a Timer Alarm in seconds

 clc; clear;

disp('This program is a timer Alarm/  by Ahmed Elkhatat');

disp('_______________________________')

n=input('Set the timer in seconds:  ');

tic;

beep;

pause (n);

beep;

toc;

msgbox('Time is up')

 

 

3.     Creating Function files in MATLAB using M.Files

Function: are files that take certain inputs and execute sequence of steps, and then returns outputs at the end.

Function files has different forms, and their syntax can be presented as following:

function output= function_name (input 1, input 2,..)

function [out 1, out2,..] = function_name (input 1, input 2,..)

function [out 1, out2,..]= function_name

function function_name (input 1, input 2,..)

function function_name

Example 1:

Create a function to find the area of a triangle when its height and base are given.

 

Note (1) :

You can use % to add comments to your script. This will be very helpful as you can recall these comments if you write the command help (function name)

Note (2):

 When You save the function, make sure that the file name is precisely the function name to execute the function correctly.

 

Example 2

Create a function to calculate the velocity of a free-falling bungee jumper, where the the velocity of a free-falling bungee jumper is defined as

Where:

Ø    v is the velocity in m/s

Ø    g is the acceleration due to gravity (9.81 m/s²)

Ø    m is mass in kg

Ø    Cd is the drag the coefficient in kg/m

Ø    t is time in sec

 

 

If you want to create a function without an output (i.e., to assign the output later as a display the message, then you can write the function in this form

function function_name (input 1, input 2,..)

function bungeevel1(m,t,cd);

 

 Example 3:

Create a function to calculate the loss coefficient and head loss of a pipe when friction factor, pipe length, pipe diameter, and fluid velocity are given

 

Where:

Ø    v is velocity in m/s

Ø    g is the acceleration due to gravity (9.81 m/s²)

Ø    f the friction factor (fanning)

Ø    L is the pipe length (m)

Ø    D is the pipe diameter (m)

Ø    Kf is the loss coeffient  

Ø    HL is the head loss (m)

 

Note that you got only one value, so in order to get the other values, the function should be written as

Another way to create the function file using

function function_name (input 1, input 2,..)

 

4.     Loops and Conditions using (If expression) in MATLAB.

 

If expression, statements, end evaluates an expression and executes a group of statements when the expression is true. An expression is true when it is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false.

Syntax

if expression statements end

if expression else statements end

if expression statements elseif expression statements else statements end

 

Example 1:

Create M file to calculate the Body Mass Index (BMI) and inform the user what the index means using (if Condition) in a function file.

 Note:

Ø    BMI <18.5, then it is Underweight Body

Ø    18.5 < BMI < 24.9, them it is Normal Body

Ø    24.9 < BMI < 29.9 it is Overweight Body

Ø    BMI > 29.9, then it is Obese Body

Try it using (if/ ifelse)

 

Example 2:

Create M file to show a student's name and show his Graded letter using input function and (if Condition). (Inputs is name, %, and Course Code)

__________

 

Example 3:

Create M file to calculate the labor payment according to the following rules.

100 QR/hr for the first 35 hrs.

150 QR/hr for the next 25 hrs.

200 Qr/hr for further hrs.  

 

Example 4:

Create M file to calculate the Calculate a series of students Grade letters using (Students' Scores should be inserts as an array.

 

 

 

5.     Loops and Conditions using (For expression) in MATLAB.

For loop is used to repeat a specified number of times

 

Syntax

for index = values

   statements

end

Example 1:

Example 2:

Example 3:

Note: if you want the MATLAB only to show the last value, then get disp(x) out of the loop as following

 

Example 4:

Use a For loop to calculate the factorial number.

6.     Loops and Conditions using (While expression) in MATLAB.

While loop is used to repeat when Condition is true.

 

Syntax

while expression

   statements

end

 

Example 1:

Use while loop to calculate the factorial number.

 

 

 

 

 

Practice the following

Create if loop file where one can insert his blood pressure. A message telling  him about his health status is as follows:

1)   Low blood pressure (hypotension):  If the top number (systolic)  is lower than 90 mm Hg or the bottom number (diastolic) is lower than 60 mm Hg

2)   High blood pressure (hypertension): If the top number (systolic)  is higher than 120 mm Hg or the bottom number (diastolic) is higher than 80 mm Hg

3)   Normal blood pressure: If the top number (systolic) is between (90-120) mm Hg or the bottom number (diastolic) is between (60-80) mm Hg

 

 

 

7.     IF Condition using in Excel

 

The most straightforward formula of (IF) Condition in EXCEL is

IF(logical test, value if true, value if false)

Example

For the following given data, if the value is less than 60, then show Fail, if not do nothing

Note that we put Fail between two double quotes because it's text, not value. Also the false option, we put two empty double quotes ("") to do nothing. For not equal Condition you can use <>

Example

In the same example, if the value is less than 60, then show Fail. If it is less than 70, show D. If it is less than 80, then show C, Less than 90, then show B, else show A.

In this Condition, we replace the (false value) with the new conditional as follows:

For more complicated logical tests, (and) (or) can be used as following

IF(and(logical test_1, logical test_2),value if true, value if false)

IF(or(logical test_1, logical test_2),value if true, value if false)

Example

A military college put height and weight standards for accepting new students as following (Height 160-185 Kg) and (weight 55-80 Kg). Applicants out of these ranges should be rejected.

Student ID	Height (cm)	Weight (Kg)
1698	182	102
1687	160	70
3134	181	110
1357	171	64
3776	180	60
1897	157	105
1712	163	116
1435	177	73
4448	184	80
3413	170	110

 

 

If you want to color the Accepted cells in green and the rejected cells in red, then

a)   Select the Colum you want to apply the conditional formatting.

b)   In the Home tab, select Conditional Formatting, from the drop list, select New Rule, as shown below

In the New Formatting Rule window

a)   Rule Type: Select Format only cells that contain.

b)   Edit the Rule Description: Format only cells with Specific Text and type the word or select the cell that contains the word (Rejected), then select Format.

c)    In the Format Cells window Select Fill, Choose the color, then OK

d)            Repeat the same steps to color "Accepted in Green."

End of this section