Elements ofProgramming

in Matlab

Daniel J. BodonyDepartment of Aerospace EngineeringUniversity of Illinois at Urbana-Champaign

Video 15

In this video you will learn. . .

1 What is a program?

2 Interpreted vs. Compiled Language

3 Roles of scripts and functions

4 Program Organization

5 Example: computing the area of a circle

D. J. Bodony (UIUC) AE199 IAC Video 15 2 / 8

What is a program?

A definition:

A sequence of commands written in one or more programming languagesthat instruct a computer or other device to perform a desired set of tasks.

Source code

The human-readable sequence of commands is called the source code.

D. J. Bodony (UIUC) AE199 IAC Video 15 3 / 8

What is a program?

A definition:

A sequence of commands written in one or more programming languagesthat instruct a computer or other device to perform a desired set of tasks.

Source code

The human-readable sequence of commands is called the source code.

D. J. Bodony (UIUC) AE199 IAC Video 15 3 / 8

What is a program?

Interpreted or compiled computer language

How the source code is used to instruct the computer to perform taskscomes in two forms:

interpreted language — The source code is read by an intermediateprogram that directly executes the commands. Examples: Matlab,Python

compiled language — The source code is converted into amachine-readable file, called the binary or executable, by a compiler.The binary is then executed separately by the user. Examples:Fortran, C, C++.

D. J. Bodony (UIUC) AE199 IAC Video 15 4 / 8

Interpreted vs. Compiled Language

Pros ConsInterpreted More intuitive language Slow to runCompiled Fast! Requires compilation step;

difficult to debug

Which approach you choose depends on many things:

Language features (e.g., Matlab has many easy-to-use functions forcontrolling hardware)

History (e.g., Aerospace company many have many programs alreadywritten in one language)

Community-wide acceptance of one approach (e.g., In dynamics andcontrols, Matlab is king while in computational fluid dynamics (CFD),C/C++/Fortran dominate)

D. J. Bodony (UIUC) AE199 IAC Video 15 5 / 8

Interpreted vs. Compiled Language

Pros ConsInterpreted More intuitive language Slow to runCompiled Fast! Requires compilation step;

difficult to debug

Which approach you choose depends on many things:

Language features (e.g., Matlab has many easy-to-use functions forcontrolling hardware)

History (e.g., Aerospace company many have many programs alreadywritten in one language)

Community-wide acceptance of one approach (e.g., In dynamics andcontrols, Matlab is king while in computational fluid dynamics (CFD),C/C++/Fortran dominate)

D. J. Bodony (UIUC) AE199 IAC Video 15 5 / 8

Our goals for this course

To introduce you to programming in

An interpreted language using Matlab

A compiled language using C

D. J. Bodony (UIUC) AE199 IAC Video 15 6 / 8

Roles of scripts and functions

A Matlab program will typically use:

One script m-file to control the overall behavior

One or more function m-files to perform individual tasks

The controlling script file will

use logic control (e.g., if-else and for) to call functions to performtasks

interact with the user through plots, fprintf, and error statements

organize the data

The one or more function m-files will

perform particular tasks as asked by the controlling script

convert input data into output data

D. J. Bodony (UIUC) AE199 IAC Video 15 7 / 8

Roles of scripts and functions

A Matlab program will typically use:

One script m-file to control the overall behavior

One or more function m-files to perform individual tasks

The controlling script file will

use logic control (e.g., if-else and for) to call functions to performtasks

interact with the user through plots, fprintf, and error statements

organize the data

The one or more function m-files will

perform particular tasks as asked by the controlling script

convert input data into output data

D. J. Bodony (UIUC) AE199 IAC Video 15 7 / 8

Roles of scripts and functions

A Matlab program will typically use:

One script m-file to control the overall behavior

One or more function m-files to perform individual tasks

The controlling script file will

use logic control (e.g., if-else and for) to call functions to performtasks

interact with the user through plots, fprintf, and error statements

organize the data

The one or more function m-files will

perform particular tasks as asked by the controlling script

convert input data into output data

D. J. Bodony (UIUC) AE199 IAC Video 15 7 / 8

Program Organization

Consider the simple example of writing a program to compute the area ofthe circle for a given radius, A = πr2.

An algorithm to calculate the circle’s area might include

1 Get the input (the radius)

2 Calculate the area

3 Display the results

A Matlab program would have a script m-file that called three separatefunctions to

1 prompt the user and read in the radius

2 calculate the area from the radius

3 display the results

Return to the video!

D. J. Bodony (UIUC) AE199 IAC Video 15 8 / 8

Program Organization

Consider the simple example of writing a program to compute the area ofthe circle for a given radius, A = πr2.

An algorithm to calculate the circle’s area might include

1 Get the input (the radius)

2 Calculate the area

3 Display the results

A Matlab program would have a script m-file that called three separatefunctions to

1 prompt the user and read in the radius

2 calculate the area from the radius

3 display the results

Return to the video!

D. J. Bodony (UIUC) AE199 IAC Video 15 8 / 8