Advanc e d MAT L AB Stanley Liang, PhD York University MAT L AB - - PDF document

2017‐07‐24 1

Advanc e d MAT L AB

Stanley Liang, PhD York University

MAT L AB Sc ript vs. MAT L AB F unc tio n

• Scripts are the simplest type of

program, since they store commands exactly as you would type them at the command line.

• Scripts are simply lines of

codes

• We use semi colon ‘;’ to control

the output

• Functions are more flexible

and more easily extensible.

• A Function starts with the

keyword function

• function out1, out2,.. =

funName(arg1, arg2,..) some lines of code… return out1, out2, … end

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F unc tio n Syntax

• function [y1,...,yN] = myfun(x1,...,xM)
• start with key work ‘function’
• put all the output on the left of the “=“ side, i.e. all Ys
• on the right, give an appropriate name to the function
• use a parenthesis to include all the input arguments, i.e.

all the Xs

A func tio n to c o mpute the triang le are a

• function to compute the area of a triangle for specific base and

height function y = triangleArea(base, height) y = 0.5 *base*height end

• Note that the return key word in MATLAB only ends the function
• The return key word does not return a value, because a MATLAB

function can return many outputs

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A mo re c o mple x func tio n to c o mpute the are a and the pe rime te r o f a c irc le with a g ive n radius

function [area, perimeter] = circleFun(radius) area = pi*radius^2 perimeter = 2*pi*radius return

• to get the area

– [area, ~] = circleFun(3)

• to get the perimeter

– [~,perimeter] = circleFun(3)

• to get both

– [area, perimeter] = circleFun(3)

T he branc hing struc ture – if – e lse if - e lse

• MATLAB use the if, elseif, else

statement for flow control

• The syntax is:

if [logical statement] codes … elseif [logical statement] codes… else codes… end

• We can use the if statement only
• use the if – elseif—else—end

syntax can improve coding efficiency

• The program run from the top to

the bottom, if a true logical statement is found, the program will skip the rest

• The cadToUsdTwoDirection

function

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T he ite ratio n / lo o p struc ture

• the while loop
• the loop repeats when

condition is true while logical statement codes… end

• the for loop
• the loop repeats specified

number of times for index = values codes… end

MAT L AB Data struc ture

• Cell array
• Cell array can take different types of

data and be called by indices

• CellArray_1= cell(n)
• CellArray_2=cell(sz1,…,szN)
• CellArray_3=cell(sz)
• Structure array
• Structure array can hold different

types of data and called by their names / attributes

• A structure array uses the ‘.’ to

deference the value

• str_01 = struct
• str_02 = struct(field, value)
• str_03 = struct(fields, values)
• str_04 = struct([])

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T able in MAT L AB

• A table is a data spread sheet in

MATLAB like a worksheet in an Excel workbook.

• t01 = table(var1, …, varN)

– all variables must have the save number of rows

• t02 = table(var1, …, varN, Name,

value)

– use Name—value pairs to specify row / column names

• t03 = table() – an empty table
• create a table from workspace

variables

• create a table and specify

variable names

• read / write a table from an

external CSV file by command

• read a table from an external

CSV file by menu clicks

Handling missing data

• NaN behavior ‐‐ Not a Number
• NaN Removal

– it reduces the size of your data, can be harmful is the data set need to be merged with others in the same length – When NaN elements exist in your data, they can prevent you from performing meaningful calculations. – For example, mean([1,2,3,NaN,5]); returns NaN

• two ways
• remove the NaN elements
• replace by other values (should

do the least harm)

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I de ntify missing data

• Many plotting functions treat NaN

elements appropriately as missing elements.

• In some cases, it is better to leave NaN

elements in your data set when plotting, since doing so illustrates the missing data.

• use the nnz function to count the number
• f missing data points
• Interpolating missing Data

– Piecewise Interpolation: values are predicted based on only the neighboring data points

Simple use r inte rac tio ns

• MALTAB can create simple UI

to interact with users

• input with Text prompt
• Text Output
• Write data on the screen
• Display warning message
• Display error message
• data=input(ʹEnter number of

hours: ʹ)

• name=input(ʹEnter the

employee name: ʹ,ʹsʹ); ‐‐the input must be a string

• disp(ʹMATLAB Rocksʹ)
• fprintf(ʹCost = $%d\nʹ,20)

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Cre ate simple GUI

• menu( ) ‐‐ Generate menu of choices for user

input.

• menu returns the number of the selected

menu item, or 0 if the user clicks the close button.

• Creates a modal dialog box and returns user

input in a cell array.

• Open standard dialog box for retrieving
• files. Returns the file name as a character

array ‐‐ return file name ONLY, without path

• Gathers n inputs from mouse clicks.
• Gathers n inputs from mouse clicks
• Display a message box
• Display a waiting bar
• Display warning / error dialog box
• color = menu(ʹChoose a colorʹ,

ʹredʹ,ʹblueʹ)

• value = inputdlg(ʹPlease enter a

value:ʹ)

• filename = uigetfile
• msgbox(ʹAnalysis completeʹ)
• warndlg(ʹNon‐integer values

rounded.ʹ)

• errordlg(ʹData not foundʹ)