Unexpected zeros error in MATLAB in zeros function

YouTube Comment: This MATLAB program gives me an error.  W=2.4; L=3; Delta=0.6; i=(W./Delta)+2; j=(L./Delta); T=zeros(i,j); . When I write 0.1 for Delta, there is an error for zeros statement.

Answer: When writing a new program, avoid using the semicolon as it suppresses the output. Write each line separately in a .m file and run the mfile. That way you would have noticed that “i” is turning out to be a real number. It shows up as 26.0000 but if you use format long statement, you will see that you get 25.999999999999996. You can round(i) and round(j) to the nearest integer. The reason “i” turns out to be 25.999999999999996 is because of roundoff error, as numbers and calculations get represented in binary format.

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Reading an excel file in MATLAB

Recently I taught a volunteer class to professional engineers on MATLAB.  Two of the most requested items of interest were
1. How do I read an excel file?
2. How do I do curve fitting?

We address the first question here.  It is easy to read an excel file with the xlsread command but what do you with it once the file has been assigned.  So we took a simple example of an excel spreadsheet where the first column consists of a student number and the second column has the examination scores of the students.  You are asked to find the highest score.

The MATLAB program link is here.
The HTML version of the MATLAB program is here.
The Excel file used in the MATLAB program is here

It is better to download (right click and save target) the program as single quotes in the pasted version do not translate properly when pasted into a mfile editor of MATLAB or you can read the html version for clarity and sample output.

%% READING AN EXCEL SPREADSHEET IN MATLAB
% Language : Matlab 2008a
% Authors : Autar Kaw
% Last Revised : December 12, 2010
% Abstract: This program shows you how to read an excel file in MATLAB
% The example has student numbers in first column and their score in the
% second column
clc
clear all
disp(‘This program shows how to read an excel file in MATLAB’)
disp(‘Matlab 2008a’)
disp(‘Authors : Autar Kaw’)
disp(‘Last Revised : December 12, 2010’)
disp(‘http://numericalmethods.eng.usf.edu’)
disp(‘  ‘)

%% INPUTS
% We have two column data and it has headers in the first row.
% That is why we read the data from A2 to B32.
A=xlsread(‘c:\users\grades.xls’,’A2:B32′);
disp (‘The data read from the excel spreadsheet is’)
disp(A)
disp(‘  ‘)
%% SOLUTION
% Finding the number of rows and columns
sizem=size(A);
rows_A=sizem(1);
cols_A=sizem(2);
% Assigning the scores to a vector called score
for i=1:1:rows_A
    score(i)=A(i,2);
end
% Using the max command to find the maximum score
% HW: Write your own function “max”
maxscore=max(score);
% Finding which student got the highest score
for i=1:1:rows_A
   if score(i)==maxscore
       student_no=i;
       break;
   end
 % HW: What if more than one student scored the highest grade??
end
%% OUTPUT
disp(‘  ‘)
disp (‘OUTPUT’)
fprintf(‘Student Number# %g scored the maximum score of %g’,…
    student_no,maxscore)
disp(‘ ‘)

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A short online quiz for the MATLAB conditional statements

Frequent testing has been proven to be effective in learning.  Here we have an online quiz on MATLAB conditional statements (only if-then-else), where some of the questions are calculated (meaning that the numbers in these questions change when you retake the quiz).  So give it a try.
http://numericalmethods.eng.usf.edu/EML3041/studymate/MATLABifelseend.htm

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This post is brought to you by Holistic Numerical Methods:  Transforming Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

Subscribe to the blog via a reader or email to stay updated with this blog. Let the information follow you.

A short online quiz on the for-end loops in MATLAB

Frequent testing has been proven to be effective in learning.  Here we have an online quiz on MATLAB loops (just the for-end loops in this quiz), where some of the questions are calculated (meaning that the numbers in these questions change when you retake the quiz).  So give it a try and soon we will be adding questions on other programming basics.
http://numericalmethods.eng.usf.edu/EML3041/studymate/MATLABforendloops.htm

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This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

Subscribe to the blog via a reader or email to stay updated with this blog. Let the information follow you.

A short online quiz on MATLAB basics

Frequent testing has been proven to be effective in learning.  Here we have an online quiz on MATLAB basics, where some of the questions are calculated (meaning that the numbers in these questions change when you retake the quiz).  So give it a try and soon we will be adding questions on programming basics.
http://numericalmethods.eng.usf.edu/EML3041/studymate/matlabbasics.htm

This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

Subscribe to the blog via a reader or email to stay updated with this blog. Let the information follow you.

MATLAB code for bubble sort

In the previous blog, we spelled out the bubble sort algorithm for putting an array of numbers in an ascending order.   In this post, I am posting the matlab program. It is better to download the program as single quotes in the pasted version do not translate properly when pasted into a mfile editor of MATLAB or see the html version for clarity and sample output.

%% PUTTING AN VECTOR OF NUMBERS IN AN ASCENDING ORDER?
% Language : Matlab 2007a
% Authors : Autar Kaw
% Last Revised : November 8, 2009
% Abstract: This program shows you how to put a vector
% of numbers in an ascending order using the bubble sort method
clc
clear all
disp(‘This program shows the bubble sort method’)
disp(‘to put a vector of numbers in an ‘)
disp(‘ascending order’)
disp(‘Matlab 2007a’)
disp(‘Authors : Autar Kaw’)
disp(‘Last Revised : November 8, 2009’)
disp(‘http://numericalmethods.eng.usf.edu’)
disp(‘  ‘)
%% INPUTS
% The vector of numbers
disp (‘INPUTS’)
disp(‘Input the vector of numbers’)
A=[18  7  6  15  4  13];
disp(A)
%% SOLUTION
% Number of entries, n
n=length(A);
% making (n-1) passes
for j=1:1:n-1
    % comparing each number with the next and swapping
    for i=1:1:n-1
    if A(i)>A(i+1);
        % temp is a variable where the numbers are kept
        % temporarily for the switch
        temp=A(i);
        A(i)=A(i+1);
        A(i+1)=temp;
    end
    end
end

%% OUTPUT
disp(‘  ‘)
disp (‘OUTPUT’)
disp (‘The ascending matrix is’)
disp(A)

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This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

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Bubble sorting

Last week, I was teaching how to randomly pick lotto numbers using MATLAB.  The problem was that some of the numbers that were getting picked were identical.  We solved this by using comparisons until the current number picked is different from the previously selected numbers.  We blogged on this a few months ago.  But there is still an aesthetic problem of how the numbers are presented.  The numbers are not in an ascending or descending order.  This is a good time to show how to do this using the simplest (if not the most efficient) procedure called the bubble sort.

Let’s suppose someone asks you to put [8 7  9  5   4] in an ascending order.  

Starting from the first number, you compare the number with the next number, and see if it is greater.  If it is, you swap the numbers.  You continue to do this with the second number, third number and so on until the second last number.  What this does is bubble the largest number to the end. 

[8  7  9  5  4 ] -> [7  8  9  5  4]  (as 8>7) -> [7  8  9  5  4]  (as 8 is not > 9)-> [7  8  5   9   4]  (as 9 is >5) -> [7  8   5  4  9]  (as 9>4).  See how the largest number is at the end. 

Now repeat this.  [7  8   5  4  9]  -> [7  8  5  4  9] (as 7 is not >8] -> [7   5  8  4  9] (as 8>5) -> [7  5  4  8 9]  (as 8>4) ->  [7  5  4  8  9 ] (as 8 is not >9)

Now repeat this.  [ 7  5  4  8  9] -> [5  7  4  8  9] -> [ 5  4  7  8  9] -> [ 5  4  7  8  9]  -> [  5  4  7  8  9]

Now repeat this.  [5  4  7  8  9] -> [ 4  5  7  8  9] -> [ 4  5  7  8 9] -> [ 4  5  7  8   9]  -> [  4 5  7  8  9]

It looks like we are done.  If n is the number of the numbers in the array, it takes (n-1) swaps within each of the (n-1) repetitions.  So we do not have to guess how many swaps it takes or how many repetitions it takes. 

To make the bubble sort efficient, we can do the following: 1) Since with each repetition the largest number bubbles up, we may need to do less swaps.  For the first repetition, we will do (n-1) swaps, for the next repetition, we do the first (n-2) swaps, and so on.  2) We can also keep track of number of swaps taking place in a repetition.  If no swaps take place in a repetition, no more repetitions are needed.

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This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

Subscribe to the blog via a reader or email to stay updated with this blog. Let the information follow you.

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