/Matlab-Cheat-Sheet

Matlab cheat sheet for MACM 316

Matlab Basic

User Input

Use the built-in input function. Datatype input are just like the once in C programming

input("Sentences : ", "datatype input (%s - string, and etc)")

Example

name = input("What's your name : ", "%s");

To output string or char

fprintf(name)   % fancy print

To output a value

vec = [1 2 3]
disp(vec)

Variables / Data Types

  • Variables start with a letter and then numbers
  • Data types are classes which also have associated methods for working with that data
    • Types include int8, int16, int32, int64, char, logical (boolean), double, single (generic int) and unsigned uint8, ...

Declaring variable is like Python (no need to put datatypes in front)

var = 'String'

class function display the data type

var = 'String'
class(var)  % 'string' - char and "string" - string

Boolean map true as 1 and false as 0

5 > 2
b1 = true

Show max and min value

intmin('int8')
intmax('int8')

Find largest double

realmax

Find largest integer

realmax('single')

You can continue the expressions into newline using ...

v1 = 1 + 2 + 3 ...
+ 4

Casting

Everything defaults to double

v2 = 8
class(v2)
>>> ans = 
        'double'

Cast to int8

v3 = int8(v2)
class(v3)
>>> ans = 
        'int8'

Convert char to double

v4 = double('A')    % v4 = 65

Convert to Char

v5 = char(64)   % v5 = '@'

Math Opertors & Sprintf

sprintf formats a string

  • %d - Integers
  • %f - Floats
  • %e - exponential notation
  • %c - Characters
  • %s - Strings

Example

fprintf('5 + 4 = %d\n', 5 + 4)  % 5 + 4 = 9
fprintf('5 - 4 = %d\n', 5 - 4)  % 5 - 4 = 1
fprintf('5 * 4 = %d\n', 5 * 4)  % 5 * 4 = 20

Define your value want only 2 decimals

fprintf('5 / 4 = %0.2f\n', 5 / 4)

Exponentiation

fprintf('5^4 = %d\n', 5^4)

Modulus (Escape % by doubling)

fprintf('5 %% 4 = %d\n', mod(5,4))

Generate a random value between 10 & 20

randi([10,20])

Precision is accurate to 15 digits by default

bF = 1.1111111111111111
bF2 = bF + 0.1111111111111111
fprintf("bF2 = %0.16f\n", bF2)

Math Functions

  • Absolute value - abs(x)
  • Floor estimation - floor(x)
  • Ceiling estimation - ceil(x)
  • Rounding values - round(x)
  • Exponential (ex) - exp(x)
  • Logorithm - log(x)
  • log base 10 (log10 x) - log10(x)
  • log base 2 (log2 x) - log2(x)
  • Square root - sqrt(x)
  • Degrees to radian - deg2rad(x)
fprintf('abs(-1) = %d\n', abs(-1))   
fprintf('floor(2.45) = %d\n', floor(2.45)) 
fprintf('ceil(2.45) = %d\n', ceil(2.45))
fprintf('round(2.45) = %d\n', round(2.45))
fprintf('exp(1) = %f\n', exp(1)) % e^x
fprintf('log(100) = %f\n', log(100))
fprintf('log10(100) = %f\n', log10(100))
fprintf('log2(100) = %f\n', log2(100))
fprintf('sqrt(100) = %f\n', sqrt(100))
fprintf('90 Deg to Radians = %f\n', deg2rad(90))

Conditionals

Relational Operators: >, <, >=, ==, and ~=(Not equal)

Logical Operators: || (or), && (and), ~ (not)

age = 12

if age >= 5 && age <= 6
    disp("You're in Kindergarten")
elseif age >= 7 && age <= 13
    disp("You're in Middle School")
elseif age >= 14 && age <= 18
    disp("You're in High School")
else
    disp("Stay Home")
end

true || false % 1 (true)
~true   % false

Switch is used when you have a limited number of options

switch age
    case 5
        disp("Go to Kindergarten")
    case num2cell(6:13)
        disp("Go to Middle School")
    case {14,15,16,17,18}
        disp("Go to High School")
    otherwise
        disp("Stay Home")
end

Vectors

Vectors are either row or column vectors or 1 dimensional arrays

vt1 = [5 3 2 1]

Length of the vector

vL =  length(vt1)

Sort in ascending order

vt1 = sort(vt1)

Sort in descending order

vt1 = sort(vt1, 'descend')

Create a range

vt2 = 5:10

Create a range with a step

vt3 = 2:2:10

Concatenate vectors

vt4 = [vt1 vt2]

Get a value with an index starting at 1

vt4(1)

Get the last value

vtEnd = vt4(end)

Change a value

vt4(1) = 12

Add to the end (0 is added to indexes between)

vt4(11) = 33

Get 1st 3 values

vt4(1:3)

Get 2, 4th and 6th

vt4([2 4 6])

Create a column vector

vt5 = [2;3;4]
% And another row
vt6 = [1 2 3]

Vector multiplication

We need a column and row vector

Multiply vt6(1,1) by each row in vt5(1,:)

vtMult = vt5 * vt6

Dot Product

(1*4) + (5*2) + (3*6) = 32

vt7 = [4 5 6]

Tranposes the vector

vtDotP = vt6 * vt7'
% or
vtDotP2 = dot(vt6, vt7)

Cross Product

[a1, a2, a3] [b1, b2, b3]
(1,1) = (a2*b3) - (a3*b2)
(1,1) = (2*6) - (3*5) = -3
(2,1) = (a3*b1) - (a1*b3)
(3,1) = (a1*b2) - (a2*b1)
vtCross = cross(vt6, vt7)

Create linearly spaced vector with for elements between 1 and 20

vt8 = linspace(1,20,4)

Logarithmically spaced vector 101, 102, 103

vt9 = logspace(1,3,3)

Matrices

Matrices have rows and columns

m1 = [2 3 4; 4 6 8]

Number of values in a row

mNRV = length(m1)

Total number of values

mNV = numel(m1)

Get row and column size

mS = size(m1)

Store rows and columns in different variables

[nRows, nCols] = size(m1)

Generate random matrix with 2 rows between 10 & 20

m2 = randi([10,20], 2)

Use row then column to get a value

m2(1,2)

Change a value ``matlab m2(1,2) = 22


Change all row values
```matlab
m2(1,:) = 25

Change all column values

m2(:,1) = 36

Get 1st value in the last row

mR1Last = m2(end,1)

Get the 2nd value in last column

MR2Last = m2(2,end)

Delete the 2nd column

m2(:,2)

Looping

For loop

for i = 1:10
    disp(i)
end

Decrement and stepping

for i = 10:-1:0
    disp(i)
end

Specify values

for i = [2 3 4]
    disp(i)
end

Cycle through a matrix

m4 = [2 3 4; 4 6 8]
for i = 1:2
    for j = 1:3
        disp(m4(i,j))
    end
end

Cycle through a vector

lVect = [6 7 8]
for i = 1:length(lVect)
    disp(lVect(i))
end

While loop

i = 1
 
% Print out only evens
while i < 20
    if (mod(i,2)) == 0
        disp(i)
        
        % MatLab doesn't have ++, +=
        i = i + 1;
        
        % Skip back to the top of the loop
        continue 
    end
 
    i = i + 1;
 
    if i >= 10
        
        % Leave the loop
        break 
    end
end

Matrix Functions

sample matrix

m3 = [2 3 4; 4 6 8; 8 12 16; 16 24 32]

You can added, subtract, etc. matrice

m4 = [1:3; 4:6]
m5 = [2:4; 5:7]
 
m4 + m5
m4 .* m5

Functions perform operations on each value

sqrt(m3)
m3 = m3 * 2

Sum adds all the columns

sum(m3)

Matrix Multiplication

Columns of m6 must equal rows in m7

m6 = [1 2 3;
    4 5 6]
 
m7 = [1 1 1 1;
    2 2 2 2;
    3 3 3 3]
 
% m8(1,1) = (1*1) + (2*2) + (3*3) = 14
 
m8 = m6 * m7

Check how many values are greater then 3

gT3M = m4 > 3
sum(gT3M, 'all')

Check for equality

isequal(m4, m5)

Find matching value indexes

find(m3 > 24)

Multiply column values

prod(m3)

1st row stays the same and each after is a sum of the proceeding and current row cumsum(m3, 'reverse') starts in opposite order

cumsum(m3)

Like cumsum, but with multiplication

cumprod(m3)

Flip 1st column to last

fliplr(m3)

Flip rows

flipud(m3)

Rotate 90 degrees

rot90(m3)

Rotate 180 degrees

rot90(m3,2)

Convert into a 2 x 6 matrix

reshape(m3, 2, 6)

Duplicate matrix into new matrix 2 rows by 1 column

repmat(m3, 2, 1)

Duplicates elements into new matrix 2 rows for each value

repelem(m3, 2, 1)

Cell Arrays

Stores values of different types

cA1 = {'Doug Smith', 34, [25 8 19]}

Define the number of spaces to set aside

cA2 = cell(5)

Get by index

cA1{1}
cA1{3}(2)

Add more data

cA1{4} = 'Patty Smith'

Get size

length(cA1)

Delete a value

cA1(4) = []

Output

for i = 1:length(cA1)
    disp(cA1{i})
end

Cell Array to char matrix

cA3 = {'Doug' 'Patty'}
nameMat = char(cA3)

Char array to cell array

cA4 = cellstr(nameMat)

Strings

Strings are vectors of characters

str1 = 'I am a string'

Get length

length(str1)

Character at index

str1(1)

Get substring

str1(3:4)

Join strings (Escape ' with '')

str2 = strcat(str1, ' that''s longer')

Find all index matches for a string

strfind(str2, 'a')

Replace any matches

strrep(str2, 'longer', 'bigger')

Split string using delimiter ' '

strArray = strsplit(str1, ' ')
class(strArray)
strArray(1)

Convert cell array into a string

cA5 = {'I' 'like' 'chickens'}
str3 = strjoin(cA5)

Integer to string

nStr = int2str(99)

Float to str

fStr = num2str(3.14)

Compare for equality

strcmp(str1, str2)

Check if is a character

isletter('num 2')

Check if all are letters ('alphanum' letters or numbers)

isstrprop('word2', 'alpha')

Is it a string

ischar('Some words 2')

Sort ascending (, 'descend')

sort(str3)

Delete whitespace

strtrim(str1)

Uppercase & lowercase

lower(str1)
upper(str1)

Structures

Custom data type that stores related data in fields

dougSmith = struct('name', 'Doug Smith', ...
    'age', 34, 'purchases', [12 23])

Access data

disp(dougSmith.age)

Add a field

dougSmith.wife = 'Patty Smith'

Remove a field

dougSmith = rmfield(dougSmith, 'wife')

Check for a field

isfield(dougSmith, 'wife')

Get fields

fieldnames(dougSmith)

Store structs in a vector

customers(1) = dougSmith
sallySmith = struct('name', 'Sally Smith', ...
    'age', 34, 'purchases', [18])
customers(2) = sallySmith

Get data

disp(customers(2).name)

Tables

Tables are labeled rows of data in a table format

name = {'Jim'; 'Pam'; 'Dwight'};
age = [28; 27; 31];
salary = [35000; 26000; 75000];
id = {'1', '2', '3'};

RowNames defines the name used for each row

employees = table(name, age, salary, 'RowName', id)

Get avg salary

meanSalary = mean(employees.salary)

Add column of data

employees.vDays = [10; 14; 16]

Show just 2 by id

employees({'1', '2'},:)

Get by name

employees(ismember(employees.name,{'Jim' 'Dwight'}), :)

File I/O

Generate a random 8x8 matrix between 10 & 50

randM = randi([10,50], 8)

Save the file as a text file and overwrite

save sampdata.dat randM -ascii

Read the data into a matrix with the same name as the data file

load sampdata.dat
disp(sampdata)

Display file data

type sampdata.dat

Saving variables to a file, save yourfile (saves every variable)

save myData

Read file

load myData
who

Append data

v4 = 123
save -append myData v4

Functions

Get cylinder volume

tic toc is used to calculate how long it took for code to execute

tic 
cylinderVol(20, 30)
toc

Try to change a variable value in a function

changeMe = 5
changeVal()
disp(changeMe)

Function with no arguments

getRandomNum

Return more then 1 value

[coneV, cylVol] = getVols(10,20)

Eval will execute code saved as a string

toExecute = sprintf("total = %d + %d", 5, 4)
eval(toExecute)

Except a variable number of arguments

theSum = getSum(1, 2, 3, 4)

Return a variable number of values

listOfNums = getNumbers(10)

Create a function that finds the volume of a cylinder

% Format 
function returnVar = funcName(arguments)
 
% Example
function vol = cylinderVol(radius, height)
vol = pi * radius^2 * height
end

Try to change a variable value in a function

If you return nothing leave it out

function changeVal()
% This is a local or variable specific to the function
 
changeMe = 10
class(changeMe)
end

Return a random value

function randNum = getRandomNum
randNum = randi([1,100])
end

Return multiple volumes

function [coneVol, cylinVol] = getVols(radius, height)
cylinVol = pi * radius^2 * height
coneVol = 1/3 * cylinVol
end

Variable arguments stored in varargin

function sum = getSum(varargin)
sum = 0;

% Cycle through contents while adding

for k = 1:length(varargin)
    sum = sum + varargin{k}(1);
end
end

Returns a variable number of values

function [varargout] = getNumbers(howMany)
for k = 1:howMany
    varargout{1}(k) = k;
end
end

Receives a function

function sol = doMath(func, num)
sol = func(num);
end

Return a function

function func = doMath2(num)
func = @(x) x * num;
end

Every recursive function must reach a point where it no longer makes a function call

function val = factorial(num)
 
if num == 1
    val = 1;
else
    val = num * factorial(num - 1);
end
end

Anonymous Functions

Anonymous functions are one line functions

% Format
nameOfFunc = @ (attr) functionBody;

% Example
cubeVol = @ (l, w, h) l * w * h;
cV = cubeVol(2,2,2)

Pass function to function

mult3 = @ (x) x * 3;
sol = doMath(mult3, 4)

Return a function

mult4 = doMath2(4);
sol2 = mult4(5)

Recursive Functions

Recursive functions call themselves

Calculate factorial

1st : result = 4 * factorial(3) = 4 * 6 = 24

2nd : result = 3 * factorial(2) = 3 * 2 = 6

3rd : result = 2 * factorial(1) = 2 * 1 = 2

fact4 = factorial(4)

Object Oriented Programming (OOP)

Real world objects have attributes (height, weight) & capabilities (run, eat). Classes model real world objects by storing attributes as properties and model capabilities using methods

A class as a blueprint then creates objects

Classes must be created in their own file with class name == file name

a1 = Shape(10, 20);
disp(a1)
Shape.setGetNumShapes
a1.getArea
 
a2 = Shape(5, 10)
disp(a2)
Shape.setGetNumShapes
 
a1 > a2
 
a3 = Trapezoid(10, 4, 6);
disp(a3)
a3.getArea

Plotting

Define x & y values

xVals = 1:5
yVals = [2 4 8 5 9]
yVals2 = [1 5 7 6 8]

Creates window labeled figure 1 with plot

figure(1)

  • Colors : blue(b), black(k), cyan(c), green(g),

  • magenta(m), red(r), yellow(y), white(w)

  • Plot Symbols : . o x + * s d v ^ < > p h

  • Line Types : -, :, -., - -

Green dotted line with + at points 2 line width

plot(xVals, yVals, 'g+:','LineWidth',2)

Draw over previous plot

hold on

Draw black stars on points

plot(xVals, yVals2, 'k*')

Defines look of each plot

legend('yVals', 'yVals2')

Show grid

grid on

Define x & y lables & Title

xlabel('Days')
ylabel('Money')
title('Money made Today')

Creates window labeled figure 2 with bar chart

figure(2)
bar(xVals, yVals, 'r')