Jun

4

A 10 minute tutorial for solving Math problems with Maxima

Filed Under Essential Math, Software | 85 Comments

About 50,000 people read my article 3 awesome free Math programs. Chances are that at least some of them downloaded and installed Maxima. If you are one of them but are not acquainted with CAS (Computer Algebra System) software, Maxima may appear very complicated and difficult to use, even for the resolution of simple high school or calculus problems. This doesn’t have to be the case though, whether you are looking for more math resources to use in your career or a student in an online bachelor’s degree in math looking for homework help, Maxima is very friendly and this 10 minute tutorial will get you started right away. Once you’ve got the first steps down, you can always look up the specific function that you need, or learn more from Maxima’s official manual. Alternatively, you can use the question mark followed by a string to obtain in-line documentation (e.g. ? integrate). This tutorial takes a practical approach, where simple examples are given to show you how to compute common tasks. Of course this is just the tip of the iceberg. Maxima is so much more than this, but scratching even just the surface should be enough to get you going. In the end you are only investing 10 minutes.

Maxima as a calculator

You can use Maxima as a fast and reliable calculator whose precision is arbitrary within the limits of your PC’s hardware. Maxima expects you to enter one or more commands and expressions separated by a semicolon character (;), just like you would do in many programming languages.

(%i1) 9+7;
(%o1) 16
(%i2) -17*19;
(%o2) -323
(%i3) 10/2;
(%o3) 5

Maxima allows you to refer to the latest result through the % character, and to any previous input or output by its respective prompted %i (input) or %o (output). For example:

(%i4) % - 10;
(%o4) -5
(%i5) %o1 * 3;
(%o5) 48

For the sake of simplicity, from now on we will omit the numbered input and output prompts produced by Maxima’s console, and indicate the output with a => sign. When the numerator and denominator are both integers, a reduced fraction or an integer value is returned. These can be evaluated in floating point by using the float function (or bfloat for big floating point numbers):

8/2;
=> 4
8/2.0;
=> 4.0
2/6;
=> \displaystyle \frac{1}{3}
float(1/3);
=> 0.33333333333333
1/3.0;
=> 0.33333333333333
26/4;
=> \displaystyle \frac{13}{2}
float(26/4);
=> 6.5

As mentioned above, big numbers are not an issue:

13^26;
=> 91733330193268616658399616009
13.0^26
=> \displaystyle 9.1733330193268623\text{ }10^_{+28}
30!;
=> 265252859812191058636308480000000
float((7/3)^35);
=> \displaystyle 7.5715969098311943\text{ }10^_{+12}

Constants and common functions

Here is a list of common constants in Maxima, which you should be aware of:

  • %e - Euler’s Number
  • %pi - \displaystyle \pi
  • %phi - the golden mean (\displaystyle \frac{1+\sqrt{5}}{2})
  • %i - the imaginary unit (\displaystyle \sqrt{-1})
  • inf - real positive infinity (\infty)
  • minf - real minus infinity (-\infty)
  • infinity - complex infinity

We can use some of these along with common functions:

sin(%pi/2) + cos(%pi/3);
=> \displaystyle \frac{3}{2}
tan(%pi/3) * cot(%pi/3);
=> 1
float(sec(%pi/3) + csc(%pi/3));
=> 3.154700538379252
sqrt(81);
=> 9
log(%e);
=> 1

Defining functions and variables

Variables can be assigned through a colon ‘:’ and functions through ‘:=’. The following code shows how to use them:

a:7; b:8;
=> 7
=> 8
sqrt(a^2+b^2);
=> \sqrt{113}
f(x):= x^2 -x + 1;
=> x^2 -x + 1
f(3);
=> 7
f(a);
=> 43
f(b);
=> 57

Please note that Maxima only offers the natural logarithm function log. log10 is not available by default but you can define it yourself as shown below:

log10(x):= log(x)/log(10);
=> \displaystyle log10(x):=\frac{log(x)}{log(10)};
log10(10)
=> 1

Symbolic Calculations

factor enables us to find the prime factorization of a number:

factor(30!);
=> \displaystyle 2^{26}\,3^{14}\,5^7\,7^4\,11^2\,13^2\,17\,19\,23\,29

We can also factor polynomials:

factor(x^2 + x -6);
=> (x-2)(x+3)

And expand them:

expand((x+3)^4);
=> \displaystyle x^4+12\,x^3+54\,x^2+108\,x+81

Simplify rational expressions:

ratsimp((x^2-1)/(x+1));
=> x-1

And simplify trigonometric expressions:

trigsimp(2*cos(x)^2 + sin(x)^2);
=> \displaystyle \cos ^2x+1

Similarly, we can expand trigonometric expressions:

trigexpand(sin(2*x)+cos(2*x));
=> \displaystyle -\sin ^2x+2\,\cos x\,\sin x+\cos ^2x

Please note that Maxima won’t accept 2x as a product, it requires you to explicitly specify 2*x. If you wish to obtain the TeX representation of a given expression, you can use the tex function:

tex(%);
=> $$-\sin ^2x+2\,\cos x\,\sin x+\cos ^2x$$

Solving Equations and Systems

We can easily solve equations and systems of equations through the function solve:

solve(x^2-4,x);
=> \displaystyle \left[ x=-2 , x=2 \right]
%[2]
=> x=2
solve(x^3=1,x);
=> \displaystyle \left[ x={{\sqrt{3}\,i-1}\over{2}} , x=-{{\sqrt{3}\,i+1}\over{2}}  , x=1 \right]
trigsimp(solve([cos(x)^2-x=2-sin(x)^2], [x]));
=> \displaystyle \left[ x=-1 \right]
solve([x - 2*y = 14,  x + 3*y = 9],[x,y]);
=> \left[ \left[ x=12 , y=-1 \right]  \right]

2D and 3D Plotting

Maxima enables us to plot 2D and 3D graphics, and even multiple functions in the same chart. The functions plot2d and plot3d are quite straightforward as you can see below. The second (and in the case of plot3d, the third) parameter, is just the range of values for x (and y) that define what portion of the chart gets plotted.

plot2d(x^2-x+3,[x,-10,10]);

2dplot.png

plot2d([x^2, x^3, x^4 -x +1] ,[x,-10,10]);

many_2dplot.png

f(x,y):= sin(x) + cos(y);
plot3d(f(x,y), [x,-5,5], [y,-5,5]);

3dplot.png

Limits

limit((1+1/x)^x,x,inf);
=> %e
limit(sin(x)/x,x,0);
=> 1
limit(2*(x^2-4)/(x-2),x,2);
=> 8
limit(log(x),x,0,plus);
=> -\infty
limit(sqrt(-x)/x,x,0,minus);
=> -\infty

Differentiation

diff(sin(x), x);
=> \displaystyle cos(x)
diff(x^x, x);
=> \displaystyle x^{x}\,\left(\log x+1\right)

We can calculate higher order derivatives by passing the order as an optional number to the diff function:

diff(tan(x), x, 4);
=> \displaystyle 8\,\sec ^2x\,\tan ^3x+16\,\sec ^4x\,\tan x

Integration

Maxima offers several types of integration. To symbolically solve indefinite integrals use integrate:

integrate(1/x, x);
=> \displaystyle log(x)

For definite integration, just specify the limits of integrations as the two last parameters:

integrate(x+2/(x -3), x, 0,1);
=> \displaystyle -2\,\log 3+2\,\log 2+{{1}\over{2}}
integrate(%e^(-x^2),x,minf,inf);
=> \sqrt{\% pi}

If the function integrate is unable to calculate an integral, you can do a numerical approximation through one of the methods available (e.g. romberg):

romberg(cos(sin(x+1)), x, 0, 1);
=> 0.57591750059682

Sums and Products

sum and product are two functions for summation and product calculation. The simpsum option simplifies the sum whenever possible. Notice how the product can be use to define your own version of the factorial function as well.

sum(k, k, 1, n);
=> \displaystyle \sum_{k=1}^{n}{k}
sum(k, k, 1, n), simpsum;
=> \displaystyle {{n^2+n}\over{2}}
sum(1/k^4, k, 1, inf), simpsum;
=> \displaystyle {{\%pi^{4}}\over{90}}
fact(n):=product(k, k, 1, n);
=> fact(n):=product(k,k,1,n)
fact(10);
=>  3628800

Series Expansions

Series expansions can be calculated through the taylor method (the last parameter specifies the depth), or through the method powerseries:

niceindices(powerseries(%e^x, x, 0));
=> \displaystyle \sum_{i=0}^{\infty }{{{x^{i}}\over{i!}}}
taylor(%e^x, x, 0, 5);
=> \displaystyle 1+x+{{x^2}\over{2}}+{{x^3}\over{6}}+{{x^4}\over{24}}+{{x^5}\over{120 }}+\cdots

The trunc method along with plot2d is used when taylor’s output needs to be plotted (to deal with the +\cdots in taylor’s output):

plot2d([trunc(%), %e^x], [x,-5,5]);

taylor.png

I hope you’ll find this useful and that it will help you get started with Maxima. CAS can be powerful tools and if you are willing to learn how to use them properly, you will soon discover that it was time well invested.

Jun

2

3 awesome free Math programs

Filed Under Software | 80 Comments

Mathematical software can be very expensive. Programs like Mathematica, Maple and Matlab are incredibly powerful, flexible and usually well documented and supported. Their price tags however are a big let down for many people, even if there are cheap (in some cases crippled) versions available for educational purposes (if you are a student or a teacher). The secondary disadvantages are those caused by the fact that such programs are proprietary. This can also affect or limit a “sharing oriented” environment like the academic and research fields. In this short article I propose well known programs that will give you a lot of flexibility and math crunching fun. And with no cost, they are great for all the different careers with a math degree. All of them have advantages and drawbacks and none of them can be considered perfect or infallible, but I consider them some of the best available today in their respective categories. They are rather general purpose softwares, but there are plenty of other specialized open source programs if you have specific needs. I’ve chosen one program for each of the 3 macro categories: symbolic, numeric and statistical computing, but you can expect quite a bit of overlapping and shared functionalities. Try the three of them, try the suggested alternatives and settle with the ones that you like and that meet your needs the best.

1. Maxima

A general purpose CAS (Computer Algebra System) is a program that’s able to perform symbolic manipulation for the resolution of common problems. As a matter of fact, modern CAS covers an extremely wide range of functionalities. Maple is a prime example of a commercial CAS software. In this category I’d say that Maxima is an excellent open source cross platform tool. wxMaxima is a good GUI version (possibly the best one on Windows), but other front-ends exist. The 3D plot below was generated by Maxima.

3D Chart from Maxima

Valuable mentions are:

2. Scilab

Matlab is the standard for numerical computing, but there are a few clones and valid alternatives that are entirely free. Scilab is the closest that you can get to Matlab without spending a penny. It’s very compatible with Matlab (albeit not 100%) but it’s really flexible, powerful and comes with a Matlab converter and Scicos which is a block diagram modeler and simulator.

scilab3d.png

Valid alternatives are:

3. R

For statistical computing and analysis in the Open Source world, it doesn’t get any better than R. It is a programming language and environment that enables you to do pretty much anything that the commercial software (S-Plus) does. It is so widely adopted that it can be considered a standard in the field.

R plot

As usual, please feel free to share your experiences and add your suggestions to enrich the discussion.

May

26

What kind of Math did they teach you?

Filed Under Essential Math, Math Education | 15 Comments

Last week “Digg effect” had quite an impact on my hosting provider. So much so that they kindly (sic) pulled the site off the web after 10 minutes of Digg love, without even bothering to send me a warning or any notification. When I complained they told me, “let us know when you are off digg”. Yes, we all know that the Tera bytes of traffic that they promise you are fictitious, but I was naively expecting better customer care, especially after having referred about a hundred clients to them. By the way, my programming blog that’s hosted with them as well, has been previously on the frontpage of Reddit, Del.icio.us, and even Slashdot and I’ve never experienced any problems (caching does wonders). But the traffic load generated by Digg was too “fast and furious” for them to cope with.

It’s not all bad though; in fact I was already planning to switch to a more serious provider with VPS or dedicated server plans. After endless research I picked Liquid Web which is fully managed, provides root access and support 24/7 on the phone. So far so good, they worked quite a bit on tweaking my server and I’ve actually called them at 3 and 5 AM and got a person on the phone in less than 30 seconds. I don’t know how well they will be able to cope with the “Digg effect” though, only time will tell.

With my “Refresh your High School Math” article on the front page of several social websites, the amount of feedback received has been terrific. It also allowed me to confirm a theory that I’ve always thought about: there is little consistency and standardization in the teaching of mathematics. I say this because the reactions to my basic math test were very highly varied. Many people said they were not able to solve the problems. That’s sad given the admittedly basic nature of the questions, but it wasn’t a big surprise. You could consider it the FizzBuzz of mathematics. What strikes me the most though, is how many people considered the test to be rightfully “middle school” material and far too basic (except for some parts of it), while others argued that it was way too advanced and too difficult for high school mathematics. This variety of reactions shows that the topics and depth of coverage in math classes in high school are quite different throughout the world.

So I’d like to explicitly ask a question to my readers, what topics did you cover while studying mathematics in high school and in what state/country were you? Please use the comment section to answer, thank you. ;-)

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