Python-3.4.3/C2/Using-plot-command-interactively/English-timed
From Script | Spoken-Tutorial
| 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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| 11:00 | The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India. |
| 11:07 | This is Usha from IIT Bombay, signing off. Thanks for watching. |
