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+.. 4.1 LO: getting started with arrays (2) [anoop]
+.. ------------------------------------------------
+.. * why arrays
+.. + speed - simply say
+.. + array level operations
+.. * creating arrays
+.. + direct data
+.. + list conversion
+.. + homogeneous
+.. + builtins - identitiy, zeros,
+.. * array operations
+.. + =+ - * /=
+
+===========================
+Getting started with Arrays
+===========================
+
+{{{ show the welcome slide }}}
+
+Welcome to the spoken tutorial on getting started with arrays.
+
+{{{ switch to next slide, outline slide }}}
+
+In this tutorial, we will learn about arrays, how to convert a list
+into an array and also why an array is preferred over lists. And array
+operations.
+
+{{{ switch to next slide on overview of array }}}
+
+Arrays are homogeneous data structures, unlike lists, arrays cannot
+have heterogeneous data elements, that is, it can have only one type
+of data type, either all integers, or strings, or float, and not a
+mix.
+
+Arrays are really fast in mathematical operations when compared to
+lists, it is at least 80 to 100 times faster than lists.
+
+{{{ switch to the next slide, creating arrays }}}
+
+Now let us see how to create arrays.
+
+I am assuming that you have your IPython interpreter running with the
+``-pylab`` option, so that you have the required modules loaded.
+
+To create an array we will use the function ``array()`` as,
+::
+
+ a1 = array([1,2,3,4])
+
+Notice that here we created a one dimensional array. Also notice the
+object we passed to create an array. Now let us see how to create a
+two dimensional array. Pause here and try to do it yourself before
+looking at the solution.
+
+This is how we create two dimensional arrays.
+::
+
+ a2 = array([[1,2,3,4],[5,6,7,8]])
+
+Let us see an easy method of creating an array with elements 1 to 8.
+::
+
+ ar = arange(1,9)
+
+And it created a single dimensional array of elements from 1 to 8.
+::
+
+ print ar
+
+And how can we make it a two dimensional array of order 2 by 4. Pause
+here and try to do it yourself, try ``ar.tab`` and find a suitable
+method for that.
+
+We can use the function ``reshape()`` for that purpose and it can be
+done as,
+::
+
+ ar.reshape(2,4)
+ ar.reshape(4,2)
+ ar = ar.reshape(2,4)
+
+Now, let us see how to convert a list object to an array. As you have
+already seen, in both of the previous statements we have passed a
+list, so creating an array can be done so, first let us create a list
+``l1``
+::
+
+ l1 = [1,2,3,4]
+
+Now we can convert the list to an array as,
+::
+
+ a3 = array(l1)
+
+
+{{{ switch to the next slide, problem statement of unsolved exercise 1 }}}
+
+Create a three dimensional array of the order (2,2,4).
+
+{{{ switch to the next slide, shape of an array }}}
+
+To find the shape of an array we can use the object ``.shape``, let us
+check the shape of the arrays we have created so far,
+::
+
+ a1.shape
+
+``a1.shape`` object is a tuple, and since a1 is a single dimensional
+array, it returned a tuple (4,).
+
+{{{ switch to the next slide, unsolved exercise 2 }}}
+
+Find out the shape of the other two arrays that we have created.
+
+{{{ Array can have only a single type of data }}}
+
+Now let us try to create a new array with a mix of elements and see
+what will happen,
+::
+
+ a4 = array([1,2,3,'a string'])
+
+Well, we expected an error as previously I said that an array can have
+only homogeneous elements, but it didn't give an error. Let us check
+the values in the new array created. In your IPython terminal type,
+::
+
+ a4
+
+Did you notice it,
+
+{{{ highlight all the array elements one by one using mouse
+movements }}}
+
+all the elements have been implicitly type casted as string, though
+our first three elements were integers.
+
+{{{ switch to the next slide, identity & zeros methods }}}
+
+An identity matrix is a square matrix in which all the diagonal
+elements are one and rest of the elements zero. We can create an
+identity matrix using the method ``identity()``.
+
+The function ``identity()`` takes an integer argument,
+::
+
+ identity(3)
+
+As you can see the identity method returned a three by three square
+array with all the diagonal elements as one and the rest of the
+elements as zero.
+
+``zeros()`` function accepts a tuple, which is the order of the array
+we want to create, and it generates an array with all elements zero.
+
+{{{ switch to the next slide, problem statement of the solved exercise
+1 }}}
+
+Let us creates an array of the order four by five with all the
+elements zero. We can do it using the method zeros,
+::
+
+ zeros((4,5))
+
+Notice that we passed a tuple to the function zeros.
+
+{{{ switch to next slide, learning exercise }}}
+
+We learned two functions ``identity()`` and ``zeros()``, find out more
+about the functions ``zeros_like()``, ``ones()``, ``ones_like()``.
+
+{{{ switch to next slide, array operations }}}
+
+Try the following, first check the value of a1,
+::
+
+ a1
+
+``a1`` is a single dimensional array, and now try,
+::
+
+ a1 * 2
+
+It returned a new array with all the elements multiplied by 2.
+::
+
+ a1
+
+note that the value of a1 still remains the same.
+
+Similarly with addition,
+::
+
+ a1 + 2
+
+it returns a new array, with all the elements summed with two. But
+again notice that the value of a1 has not been changed.
+::
+
+ a1
+
+You may change the value of a1 by simply assigning the newly returned
+array as,
+::
+
+ a1 += 2
+
+Notice the change in elements of a,
+::
+
+ a
+
+We can use all the mathematical operations with arrays, Now let us try
+this
+::
+
+ a1 = array([1,2,3,4])
+ a2 = array([1,2,3,4])
+ a1 + a2
+
+Returns an array with element by element addition,
+::
+
+ a1 * a2
+
+Returns an array with element by element multiplication, notice that
+it does not perform matrix multiplication.
+
+{{{ switch to next slide, recap slide }}}
+
+So this brings us to the end of this tutorial, in this tutorial we
+covered basics of arrays, how to create an array, converting a list to
+an array, basic array operations etc.
+
+{{{ switch to next slide, thank you }}}
+
+Thank you!
+
+.. Author: Anoop Jacob Thomas <anoop@fossee.in>
+ Reviewer 1:
+ Reviewer 2:
+ External reviewer: