Division Example

2x - 3y + 4z = 10 x + 6y - 3z = 4 -5x + y + 2z = 3

A*X = B where

A = 2 -3 4 1 6 -3 -5 1 2 B = 10 4 3 >> X = A\B X = 1.2609 2.2261 3.5391 >> 2*X(1) -3*X(2) + 4*X(3) ans = 10

Element by Element Operators

Multiplication .* x(n) = A(n)*B(n) Division ./ x(n) = A(n)/B(n) Exponentiation .^ x(n) = A(n)^y(n) Left Division .\ x(n) = B(n)/A(n)

x = A .*B x = A ./ B x = A .^ y x = A .\B

EGR 106 – Week 4 – Files

Saving commands as simple “programs” Using Matlab’s editor Useful script commands Saving and reading data

Textbook chapter 4, pages 77-100

So far:

Commands typed in the command window: – Executed by pressing “enter”– Edited using the arrow keys or

the history window Results are temporary:

– Rerun commands– Keep a “diary” file

Scripts or m files

Data files

Script Concept

A file containing Matlab commands – Can be re-executed – Are easily changed

Commands are executed in sequence– Results appear in the command window (or use ; )– File is executed by typing its name (without .m)

Can be created using any text editor – .m extension– Listed in current directory window

Matlab’s Built-in, Color Editor:

Can create a new file or open an existing m file (icons or click on file name)

Color used to aid in file creation (command types, typos)

•typical windows menu•line numbers •“run” button or F5 •debug capability

•comment lines

•note use of semicolons

•note use of colors

Where Matlab Looks for Things

1. As a variable in the current workspace

2. As a built in function

3. As an m file in the “current directory”

• Down the “search path” of directories

• Conclusion – use unique names

How Scripts Get Data

From arrays in the current workspace From arrays defined in the script Using the “input” command:

– Numeric:

x = input(' how many? ')– String:

x = input(' name? ', 's')

How Scripts Shows Data

Command of the array name Using the display command:

– Existing array – disp(x)– Text

disp(' The task is done ')

•Example:

•Note that disp shortens the resulting output by dropping the array name and removing blank lines

•Formatted print command

fprintf(format,data)•Combines text and data

•Allows complete control of the output

•format is a string (in quotes) containing text and control commands (using \ or %) – like in C

•An example:

\n = new line%d = put data here

The data itself

•Escape characters: •New line ( \n ), backspace ( \b ), tab ( \t ), …

•Conversion codes for data:•Decimal ( %d ), character ( %c ), exponential notation ( %e ), fixed precision ( %f ), … •Can add field width and precision information:

5 characters wide, 2 after the decimal point

•fprintf works element-by-element on array data:

\n added for line return

•fprintf can also write to a file:

fid = fopen( 'name', 'w' )

fprintf(fid,format,data)

…

fclose(fid)

•fid is a variable name to specify which file •name is the name of the file

w indicates “write”

Example Scripts

Matlab Data Files (not in the text)

Types:– ascii = regular text files– .mat = Matlab’s proprietary format (multiple variables)

•Saving data:•save filename•save filename array1 array2•save filename –ascii

•Reading in (loading) data:•load filename•load filename array1 array2 •load filename –ascii

Debugging Errors

Syntax errors:

Note red text = bad news

•Run-time errors: inf or NaN results

Note black text = is okay

•Logical errors in your program – hard to find•Example: quadratic equation solver

•But x2+2x+1 = (x+1)2 x = -1

•Use the built-in debugger

Missing parentheses

New Homework Procedure

Electronic submission via e-mail One single m file: executing it should

– Present solutions in order– Pause in between problems– Use clear, clc, and clf to clear out old data,

results, and/or plots– Use ; to suppress unnecessary outputs– Name file as yourlastname_4.m