#### Overview of this book

Today's world of science and technology is all about speed and flexibility. When it comes to scientific computing, NumPy is on the top of the list. NumPy will give you both speed and high productivity. "NumPy Cookbook" will teach you all about NumPy, a leading scientific computing library. NumPy replaces a lot of the functionality of Matlab and Mathematica, but in contrast to those products, it is free and open source. "Numpy Cookbook" will teach you to write readable, efficient, and fast code that is as close to the language of Mathematics as much as possible with the cutting edge open source NumPy software library. You will learn about installing and using NumPy and related concepts. At the end of the book, we will explore related scientific computing projects. This book will give you a solid foundation in NumPy arrays and universal functions. You will also learn about plotting with Matplotlib and the related SciPy project through examples. "NumPy Cookbook" will help you to be productive with NumPy and write clean and fast code.
NumPy Cookbook
Credits
www.PacktPub.com
Preface
Free Chapter
Winding Along with IPython
Get to Grips with Commonly Used Functions
Connecting NumPy with the Rest of the World
Audio and Image Processing
Special Arrays and Universal Functions
Profiling and Debugging
Quality Assurance
Speed Up Code with Cython
Index

## Finding palindromic numbers

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is `9009 = 91 x 99`. Let's try to find the largest palindrome made from the product of two 3-digit numbers.

### How to do it...

We will create an array to hold 3-digit numbers from 100 to 999 using our favorite NumPy function `arange`.

1. Create a 3-digit numbers array.

Check the first and last element of the array with the `assert_equal` function from the `numpy.testing` package:

```a = numpy.arange(100, 1000)
numpy.testing.assert_equal(100, a[0])
numpy.testing.assert_equal(999, a[-1])```
2. Create the products array

Now, we will create an array to hold all the possible products of the elements of the 3-digits array with itself. We can accomplish this with the `outer` function. The resulting array needs to be flattened with `ravel`, to be able to easily iterate over it. Call the `sort` method on the array to make sure the array is properly sorted. After that, we can do some sanity checks...