Tag Archives: arithmetic

Learn About Descriptive Statistics

I had been meaning to write a script and blog post on descriptive statistics for some time now, but with work and winter weather and the extra work that winter weather brings, and now that the winter weather is over trying to get back into an exercise routine (running up a hill is such a challenging experience, but when I get to the top of that hill I feel like Rocky Balboa on the steps at the steps at the entrance of the Philadelphia Museum of Art), I haven’t had the time to devote to this site that I would have liked. Well, that’s not entirely true. I have still been programming in my spare time. I just haven’t been able to share it here. I went to a conference in February and in my down time, I was able to write a script on descriptive statistics that I think gives a nice introduction to the area.

Before I go into descriptive statistics though, lets talk about statistics, which is concerned with the collection, analysis, interpretation and presentation of data. Statistics can generally be broken down into two categories, descriptive statistics and infernalinferential statistics, depending on what we would like to do with that data. When we are concerned with visualizing and summarizing the given data, descriptive statistics gives methods to operate on this data set. On the other hand, if we wish to draw conclusions about a larger population from our sample, then we would use methods from inferential statistics.

In the script on descriptive statistics I’ve written, I consider three different types of summaries for descriptive statistics:

Measures of Central Tendency
Mean – the arithmetic average of a set of values
Median – the middle number in a set of values
Mode – the most used number in a set of values

Dispersion
Maximum – the largest value in the data set
Minimum – the smallest value in the data set
Standard Deviation – the amount of variation in a set of data values
Variance – how far a set of numbers is spread out

Shape
Kurtosis – how peaked or flat a data set is
Skewness – how symmetric a data set is

Plots
Histogram Plots – a bar diagram where the horizontal axis shows different categories of values, and the height of each bar is related to the number of observations in the corresponding category.
Box and Whisker Plots – A box-and-whisker plot for a list of numbers consists of a rectangle whose left edge is at the first quartile of the data and whose right edge is at the third quartile, with a left whisker sticking out to the smallest value, and a right whisker sticking out to the largest value.
Stem and Leaf Plots – A stem and leaf plot illustrates the distribution of a group of numbers by arranging the numbers in categories based on the first digit.

Polynomial Arithmetic

Polynomial Arithmetic Image

With students beginning to attend classes across the nation, I wanted to focus the site towards some of the things they’re going to be addressing. This latest page publicize some scripts that I wrote to help with polynomial arithmetic. Originally I wrote these as homework exercises for a class in programming, but I have found them useful ever since – both in teaching mathematics classes like college algebra, which spends a lot of attention on polynomials, and in my research life. Its funny (and sad) the number of simple errors that a person (mathematician or not) can make when performing simple arithmetic, so I found it very useful to have a calculator more advanced than the simple scientific calculators that are so easily available.

I’m not going to spend a lot of time discussing the importance of polynomials, or trying to justify their need. I will bring up some problems that I’d like to address in the future, that deal with polynomials. The first is finding the roots of the characteristic polynomial of a matrix. This is useful in research because these roots are the eigenvalues of the matrix and can give many properties of the matrix. There are also some data analysis tools like Singular Value Decomposition and Principal Component Analysis where I will probably build out from this initial set of instances.

The user interface for the scripts I’ve written generate two polynomials and ask the user what is to be done with those polynomials. The options are to add the two, subtract polynomial 2 from polynomial 1, multiply the two, divide polynomial 1 by polynomial 2, and divide polynomial 2 by polynomial 1. There is also the option to make the calculations more of a tutorial by showing the steps along the way. Users who want new problems can generate a new first or second polynomial and clear work.

For addition and subtraction, the program works by first ensuring that both polynomials have the same degree. This can be achieved by adding terms with zero coefficient to the lower degree polynomial. Once this has been accomplished, we simply add the terms that have the same exponent.

For multiplication, the program first builds a matrix A, where the element ai, i+j on row i and column i+j of the matrix A is achieved by multiplying the ith term of the first polynomial by the jth term of the second polynomial. If an was not given a value in the matrix, then we put a value of zero in that cell. Once this matrix is formed, we can sum the columns of the matrix to arrive at the final answer.

The division of two polynomials works first by dividing the first term of the numerator by the first term of the denominator. This answer is then multiplied by the denominator and subtracted from the numerator. Now, the first term in the numerator should cancel and we use the result as the numerator going froward. This process is repeated as long as the numerator’s degree is still equal to or greater than the denominator’s degree.

Check out the latest page on polynomial arithmetic and let me know what you think.

Arithmetic Sequences

Arithmetic Sequences

I’ve added a script which helps to understand arithmetic sequences.

At a previous job of mine, there was a policy of holding a dinner party for the company each time we hired a new employee. At these dinners, each employee was treated to a $20 dinner at the expense of the company. There was also a manager responsible for keeping track of the costs of these dinners.

In computing the costs, the manager noticed that each time there is a new dinner, it was $20 more expensive than the last one. So if we let a1 represent the cost of the first dinner, and let ai represent the cost of the ith dinner, then we see that ai = ai-1 + 20. Sequences like this, where t arise quite often in practice and are called arithmetic sequences. An arithmetic sequence is a list of numbers where the difference between any two consecutive numbers is constant.

For the example above, the term an will represent the cost of dinner after the nth employee has joined the company (assuming that no employees have left the company over this time period). Also the term Sn will represent the total cost the company has paid towards these dinners.

Before we continue with this example, consider the following table which lists the first five terms of an arithmetic sequence as well as the common difference and the first five sums of this sequence.

term number term value diff sum number sum value
a1 4 3 S1 4
a2 7 3 S2 11
a3 10 3 S3 21
a4 13 3 S4 34
a5 16 3 S5 50

One of the beauties of arithmetic sequences is that if we know the first term (a1) and the common difference (d), then we can easily calculate the terms an and Sn for any n with the following formulas:

an = a1 + d*(n – 1), where d is the common difference.
Sn = n*(a1 + an)/2

We can use these formulas to derive more information about the sequence. For example, if my manager wanted to estimate the cost of dinners once we had added 30 new employees, this would be term a30 of the sequence, which we can evaluate with the above formula by a30 = a1 + d*(n – 1) = 0 + 20*(30 – 1) = 0 + 20 * 29 = 580.

The script is available at http://www.learninglover.com/examples.php?id=33.

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