E77: INTRODUCTION TO COMPUTER PROGRAMMING FOR SCIENTISTS AND ENGINEERS

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E77 INTRODUCTION TO COMPUTER PROGRAMMING FOR
SCIENTISTS AND ENGINEERS

• Lecture Outline
• Matlab basics
• 2. Matlab as a calculator
• 3. Saving and loading files in matlab

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Matlab basis

• The default MATLAB Desktop

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Matlab basis

• Starting Matlab
• double-click the Matlab icon, or
• in a terminal window, type matlab, and return
• The Command Window and the
• Matlab prompt gtgt

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Matlab basis

• The Desktop menu
• undocking command window
• tiling other windows (command history, workspace,
  current directory, profiler)
• The File menu
• Preferences
• The Help menu

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Matlab as a calculator

• Type expressions at the gtgt, and press return
• Result is computed, and displayed as ans
• Use numbers, , , /, -, (), sin, cos, exp, abs,
  round,

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Entering Commands and Expressions

• MATLAB retains your previous keystrokes.
• Use the up-arrow key to scroll back back through
  the commands.
• Press the key once to see the previous entry, and
  so on.
• Use the down-arrow key to scroll forward. Edit a
  line using the left- and right-arrow keys the
  Backspace key, and the Delete key.
• Press the Enter key to execute the command.

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Scalar Arithmetic Operations
Symbol Operation MATLAB form
exponentiation ab ab multiplication
ab ab / right division a/b a/b \ left
division b/a a\b addition a b a
b - subtraction a - b a - b
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Order of Precedence
Precedence Operation
First Parentheses, evaluated starting with the
innermost pair. Second Exponentiation,
evaluated from left to right. Third Multiplicatio
n and division with equal precedence, evaluated
from left to right. Fourth Addition and
subtraction with equal precedence, evaluated
from left to right.
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Examples of Precedence
gtgt 8 35 ans 23 gtgt 8 (35) ans
23 gtgt(8 3)5 ans 55
gtgt 4212 8/42 ans 0 gtgt (42)12
(8/4)2 ans 0 gtgt 4212 8/(42) ans
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Special Variables and Constants
Symbol Description
ans most recent answer. eps Specifies the
accuracy of floating point precision. i,j The
imaginary unit Ö-1. Inf Infinity. NaN Indicates
an undefined numerical result. pi The number p.
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Variables and the assignment operator ()

• Use names to assign result of an expression to a
  variable
• i.e. assign the value 3 to the variable x
• Variables do not need to be declared before
  assignment
• The right-hand-side needs to be a legal Matlab
  expression
• The left-hand-side needs to be a single variable
  name

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Examples of Variables and Assignment
means
gtgt A sqrt(4) A 2
gtgt C tan(pi/4) A C 3
means
(variable A must have been defined)
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Examples of Variables and Assignment

• What is the answer to

gtgt A sqrt(4) gtgt A tan(pi/4) A
gtgt A 3

• A semicolon at the end of the RHS expression
  suppresses the display.
• However, the assignment still takes place.

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The workspace

• All variables that you create are accessible from
  the prompt gtgt
• Variables are accessed using their name as a
  reference
• Builtin Matlab commands
• gtgt who
• gtgt whos
• are used to see what is in the workspace.
• You can clear (i.e., erase) variables with the
  clear command
• gtgt clear A
• clears the variable A from the workspace.

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The workspace

• All variables that you create are accessible from
  the prompt gtgt
• Variables are accessed using their name as a
  reference
• Builtin Matlab commands
• gtgt who
• gtgt whos
• are used to see what is in the workspace.
• gtgt clear all
• clears ALL the variables from the workspace.

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Quiting Matlab

• Type quit at the prompt, or
• Select Exit Matlab from the File menu
• However

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Saving the workspace

• When you quit Matlab, the variables in the
  workspace are erased from memory.
• If you need them for later use, you must save
  them.
• gtgt save
• saves all of the variables in the workspace into
  a file called matlab.mat (it is saved in the
  current directory)

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Saving the workspace

• gtgt save Roberto
• saves all of the variables in the workspace into
  a file called Roberto.mat
• gtgt save Important A B C D
• saves the variables A, B, C and any variable
  beginning with D into a file called Important.mat

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Loading from a .mat file

• load is the opposite of save.
• It reads a .mat file, putting all variables
  contained in the .mat file into the workspace
• gtgt load
• loads all of the variables from the file
  matlab.mat

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Loading from a .mat file

• gtgt load Roberto
• loads all of the variables from the file
  Roberto.mat
• There are no known security problems with load.
• Hence, you can safely send (as attachment),
  receive and use .mat files from others.

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Summary

• MATLAB can be used as a high-end calculator
• variables can be defined and manipulated.
• Precedence left to right and , / ,
• When in doubt for precedence, use parentheses!
• Variables can be cleared, saveed and loaded.
• MATLAB has special symbols e.g. pi , ANS , j ,
  etc.