MATLAB
Output if file doesn't exist
-1
algorithm for using a file
1. open the file 2. read, write, or append from the file 3. close the file.
abs(-5)
5
plus(2,5)
7
Trace Table
A listing of the variables used in the program. Completed by writing down each value that the program assigns to a variable
fprintf( 'text', variable.....)
Allows you to format variable in a certain way. More control than disp( )
control characters
Are not printed but accomplish a task (backspace or tab)
fgetl vs fgets
Both read strings from a file one line at a time. fgets keeps any newline characters, whereas fgetl does not
reshape(A)
Changes the dimensions but keeps the same number of elements
ones(2,3)
Creates a 2 by 3 matrix of 1's
zeros(4,2)
Creates a 4 by 2 matrix of zeros
magic function M = magic(3)
Creates a matrix where the sum of each column and each row are the same. (can only have one input)
rand(n)
Creates a random matrix (nxn) of all real numbers between 0 and 1
length(A)
Determines largest dimension of matrix A
size(K)
Determines number of rows and columns in matrix K
diag(A)
Extracts all diagonal elements from a matrix
subplot(m,n,p) or subplot(mnp) or subplot mnp
Figure window is divided into m x n rectangular subplots arranged like elements in an m x n matrix. p specifies the pth window for the current plot. Numbered left to right, top to bottom
%f %e %g %d
For fprinf %f= float (decimal) %d = integer (stands for decimal integer) %c= character (one character) %s= string of characters
When does a for loop end?
For loop breaks when the loop variable exceeds the terminating value.
randn(n,m)
Gives a matrix of normally distributed random numbers
A'
Gives the transpose of matrix (changes rows to columns)
Symmetric matrix
Matrix is the same as its transpose
fprintf('___________%5.4f\n',......)
Prints a string where the variable is a float with a field width of 5 and 4 decimal places for the variable where..... would be.
How are strings enclosed?
Single quotes
empty vector [ ]
To delete an element from a vector, assign an empty vector to that element
/n
Used in fprintf statement to create a new line
vertical concatenation
Using [ ; ] semicolon separates char all need to be the same length (can use spaces), but char does this automatically
When to use a while loop
When we do not know in advance how many times we will repeat executable statements
A= 1 2 3 4 5 6 7 8 9 10 11 12 0 4 5 6 a) Extract 3rd column b) Extract 2nd & 3rd column c) Extract 2nd & 3rd rows
a) A(:,3) b) B(:,2:3) c) C(2:2:4,:)
Leading blanks
blank spaces at the beginning of a string
trailing blanks
blank spaces at the end of a string
mean(data)
calculates the average
median3Filter
calculates the median of every three values in a vector. First and last elements are left alone
fclose
closeresult = fclose(fid) closeresult = fclose('all') 0 if closes successfully, -1 if not
union(a,b)
combines the data set from vectors a and b with no repeats
strcmp(s1,s2)
compares each element of s1 to the same element of s2, returns 1 for true if they are identical and 0 if false
strncmpi(s1,s2,n)
compares n characters, ignoring case
strcmpi(s1, s2)
compares strings and ignores upper or lower case
strncmp(s1,s2,n)
compares the first n characters of strings s1 and s2. Returns 1 if they are identical, 0 if false.
str2num
convert string to number
lower
converts a string to all lowercase
upper
converts all the characters of a string to all upper case
num2str
converts number to string
hist(vec,n) or histogram(vec,n)
creates a histogram which shows the frequency of values within a vector. n = the number of bins, by default, n = 10
loglog(x,y)
creates a plot with a logarithmic scale on both axes.
semilogy(x,y)
creates a plot with a logarithmic scale on the y-axis and linear scale for the x axis
blanks(5)
creates a string of all blank spaces, in this case, 5 blank spaces
strtrim
deletes both leading and trailing blanks from a string
mode(x)
determines the number that appears most frequently in x. If there's more than one, it takes the smallest.
movie(M)
displays recorded movie frames. Frames are first captured in a loop using the built-in function getframe, and are stored in a matrix m.
pie(x)
displays the percentage that each element in vector or matrix x contributes to the sum of all elements.
bar(x,y)
displays values of y as the vertical bars, x must not have duplicate values
Order in which values in a matrix are extracted and stored
down columns. to extract and store by rows, you must use a transpose. Don't forget that matrices are CREATED row wise
barh(x,y)
draws a horizontal bar chart
stem(x,y)
draws a stem plot
area(x,y)
draws the plot as a continuous curve and fills in under the curve that is created
sort in a matrix
each individual column is sorted ex) sort(mat,2) -sorts on rows instead of columns
comet(x,y)
end result is like plot(x,y), but it displays on point at a time
xlswrite
exports data as an excel file
general form used for fopen
fid = fopen('filename', 'permission string'); permission string will be r for reading, w for writing, or a for appending.
strrep(string, oldsubstring, newsubstring)
finds all occurrences of the old substring withing the string, and replaces it with the new substring
findstr(s1,s2)
finds one string in another string, returns a vector of indices of the beginning of the strings, empty vector if none
Format of a for loop
for loop_var = first_value [:step] : last_value
General for for fscanf
fscanf(fid, 'format', [dimensions]) If there are both numbers and letters, characters will be converted to their ASCII equivalents
creating a function
function a = name_of_function(x)
grid
function that puts a grid on the graph, makes it easier to see data points.
semilogx(x,y)
generates a plot of the values of x and y, using a logarithmic scale for x and a linear scale for y
mean(x)
gives the average in the x set of numbers
Getting comments from your user made function
help name_of_function
What do you need to add for a string input?
input('Enter your name: ', 's')
linspace(x,y,n)
linspace(initial, final, number of elements) Calculates the space between each element
to read variables from a MAT-file into the base workspace
load filename variable list
outlier
number much larger or smaller than the rest of the data set, usually the result of an error
when to use load Filename.ext
only if a file has the same number of values on every line and the same type
setting a line width in a graph
plot(x, y, 'LineWidth', 3)
format for graphing
plot(x-var,y-var,line marker & line) Ex) plot(x,y, 'r--o')
Name 6 3D equivalent plot functions to 2D
plot3, bar3, bar3h, stem3, pie3, comet3
r = 1 3 5 -1 -3 -5 -7 Pull out 1,5,-3,-7
r(1:2:7) 1= first entry, 2= skip every 2, 7= 7th entry
randi([_________],____,____)
randi([range],n,m)
xlsread
reads data from an excel file
fscanf
reads formatted data into a matrix, using conversion formats such as %d for integers, %s for strings, %f for floats
textscan
reads text data from a file onto column vectors stored in a cell array, also uses conversion format
deblank
removes trailing blanks
r = [1:2:6, -1:-2:-7]
returns r= 1 3 5 -1 -3 -5 -7 Vector = [ initial: skip by: end]
unique(a)
returns all data in array a without any repetitions
rand(n,m)
returns an array of random numbers with n rows and m columns
length(s)
returns number of characters in a string
intersect(a,b)
returns the data common from a and b, no repetitions
setxor(a,b)
returns the data from a and b that has nothing in common, no repetition. Finds what occurs in a or b, but not both.
setdiff(a,b)
returns the data in a that is not in b, with no repetitions and sorted in order
to append a variable from a file
save -append filename variablename
How to save a file
save Filename MatrixVariableName -ascii or save Filename MatrixVariableName -ascii -append
to save all workspace variables in a file
save filename
to save just one variable
save filename variablename
sortrows
sort the rows within a column vector
sort
sorts a vector in ascending order(default) or descending order to sort descending: sort(vec, 'descending')
sort in a cell array of strings
sorts strings in alphabetical order
white space characters
space, tab, newline(\n), and carriage return
fopen
specifies the name of the file and the mode (reading/writing/appending) default is reading. always assign to a variable
std(x)
standard deviation of array x equal to the square root of the variance
cell array
stores different types of values in its elements, could be a vector or a matrix. Stores strings of different lengths. Also uses { } instead of [ ].
Horizontal Concatenation
strcat('word', 'other word') or ['word' 'other word'] *If there are trailing blanks, only [ ]will keep them
switch statement
switch case case otherwise end
median(x)
takes the number in the middle of a sorted data set. If theres an even amount, it take the average of the two middle values.
labeling a graph
title('Title of Graph')
isletter
true if the input argument is a letter of the alphabet
ischar
true if the input argument is a string or a character vector
isspace
true if the input argument is a white space character
concatenating matrices horizontally (side-by-side)
v = [A B] where A is a 3 by 2 matrix and B is a 4 by 2 matrix. They must have the same number of columns to be put side by side
concatenating matrices vertically (one on top of another)
v = [C; D] where A is a 5 by 2 matrix and B is a 5 by 3 matrix. They must have the same number of columns to be put side by side
menu function
variable = menu('Title', 'choice 1', 'choice2'...)
var(x)
variance of the variable X
when to use for loop
when we know in advance how many iterations there will be or how many times we will repeat executable statements also used if you want to repeat the process of prompting the user and reading input a specified number of times
feof(fid)
would return logical true if the end of the file has not been reached for the file identified by "fid", or logical false if not (0)
labeling a x or y-axis
xlabel('X-axis title') and ylabel('Y-axis title')
