Python-3.4.3/C2/Using-plot-command-interactively/English-timed

Time	Narration
00:01	Hello friends! Welcome to the tutorial on using plot command interactively in IPython.
00:08	At the end of this tutorial, you will be able to: create simple plots of mathematical functions, use the Plot window to study plots better.
00:20	To record this tutorial, I am using: Ubuntu Linux 14.04 operating system, Python 3.4.3 and IPython 5.1.0
00:34	Pre-requisites to practise this tutorial are - you should know how to run basic Python commands on the ipython console.
00:44	If not, for relevant Python tutorials, please visit this website.
00:50	Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.
00:58	Now, type ipython3 and press Enter.
01:05	Let us initialise the pylab package. Type: percentage pylab and press Enter.
01:16	Let's first understand what is Pylab.
01:20	Pylab is a convenient Python module which provides- plotting functionality and has mathematical and scientific functions.
01:32	After running percentage pylab in the iPython console, you will see a message- “Using matplotlib backend: TkAgg ”.
01:41	This means matplotlib is running.
01:45	But sometimes you may get an error that says- “ImportError: No module named matplotlib”.
01:55	In such cases, you have to install matplotlib and run this command again.
02:02	Let's come back to the ipython console. Type 'linspace' followed by a question mark in ipython console. Press Enter.
02:14	Please note that the command is linspace and not linespace.
02:20	The displayed information says that linspace returns evenly spaced numbers which are calculated over the interval start and stop.
02:34	Press q to exit the documentation and return to the console.
02:41	Let's try to generate 100 points from 1 to 100. Type: linspace brackets 1 comma 100 comma 100
02:58	Here, 1 is the start , 100 is the stop and the next 100 is the number of points. Now, press Enter.
03:09	As you can see, a sequence of numbers from 1 to 100 is displayed.
03:15	Now let's try to generate 200 points between 0 and 1.
03:21	We do that by typing linspace brackets 0 comma 1 comma 200 and press Enter.
03:36	Here is the expected sequence of numbers.
03:40	In linspace, the start and stop points can be integers, decimals or constants.
03:48	Let us now learn about the len function.
03:52	First we will generate 100 points between minus pi and pi.
03:58	So, type: linspace brackets minus pi comma pi comma 100 and press Enter.
04:10	Here 'pi' is a constant defined by pylab.
04:15	Now, let us save this to a variable, say t. Press Enter.
04:22	If we now type: len bracket t and press Enter, we will get the number of points between minus pi and pi.
04:32	len function gives the no. of elements present in a given sequence.
04:37	Next, let's try and plot a cosine curve between minus pi and pi.
04:43	For this, we use the plot command. Type: plot brackets t comma cos(t) and press Enter.
04:59	As you can see from the cosine plot, cos(t) gets the cosine value at every point corresponding to point t.
05:09	We can also assign the value of cos(t) to a variable cosine by typing cosine equals to cos(t). Press Enter.
05:21	And then plot by typing plot(t comma cosine) and press Enter.
05:31	To clear the plot, we have to use the clf() function. This avoids overlapping of new plots over older plots.
05:42	In the console, type: clf() and press Enter. The previous plot is cleared and a blank plot window is displayed.
05:56	Now, let's try to plot a sine plot.
06:00	Type: plot brackets t comma sin(t) and press Enter. A sine plot is displayed.
06:14	To study the plot better on the plot window, we can use various options that are available on it. Let us have a look at these options.
06:25	Moving the mouse pointer along the plot gives us the location of each point on the plot.
06:33	Notice here, at the bottom left of the window, there are a few buttons.
06:39	The right-most among them is for saving the file. Just click on it and type the file name.
06:47	Let us save the plot by the name sin underscore curve in pdf format.
06:54	Click on the dropdown here. As you can see, there are many formats in which to save the file. Formats like png, eps, pdf, and ps are available.
07:08	We have to specify the format that we prefer at the time of saving.
07:14	To the left of the save button, is the slider button. Using this button, we can specify the margins of the plot window.
07:24	To the left of the slider button is the zoom button . It is used to zoom into the plot. Just specify the region to zoom into.
07:37	The button to the left of zoom, can be used to move the axes of the plot.
07:41	The next two buttons with left and right arrow icons, change the state of the plot.
07:48	It takes us to the previous or next state of the plot. It acts like the back and forward button in a browser.
07:57	The last one is 'home', referring to the initial plot.
08:03	Pause the video here, try out the following exercise and then resume the video.
08:09	Plot (sin(x) multiplied by sin(x)) divided by x. 1. Save the plot as sinsquarebyx dot pdf. 2. Zoom and find the maxima. 3. Bring it back to initial position.
08:26	This brings us to the end of this tutorial. In this tutorial, we have learnt to: start IPython with pylab, use the linspace function to create equally spaced points in a region,
08:42	find the length of sequences using len function, plot mathematical functions using plot, clear drawing area using clf.
08:53	usage of buttons in the UI of the plot window such as - save, zoom, move axis, back and forward, Home.
09:04	Here are some self assessment questions for you to solve - 1. Create 100 equally spaced points between minus pi by 2 and pi by 2.
09:15	2. How can we find the length of a sequence ?
09:19	3. What will the command linspace(minus pi comma pi comma 100) do?
09:26	And the answers are- We use the command linspace(minus pi by 2 comma pi by 2 comma 100) to create 100 equally spaced lines between the points minus pi by 2 and pi by 2.
09:43	len(sequence underscore name) is the function used to find out the length of a sequence.
09:50	The command linspace(minus pi comma pi comma 100) will return 100 evenly spaced samples from -pi to pi including both minus pi and pi.
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11:07	This is Usha from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

Pratik kamble, Sandhya.np14