Python/C2/Using-the-plot-command-interactively/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:00 | Hello friends and welcome to the tutorial on creating simple plots using iPython. |
| 00:06 | I hope you have iPython running on your computer. |
| 00:10 | At the end of this tutorial, you will be able to:
Create simple plots of mathematical functions. Use the Figure window to study plots better. |
| 00:20 | Let's start ipython. |
| 00:22 | Open the terminal and type: ipython -pylab and hit Enter. |
| 00:35 | Pylab is a python library which provides plotting functionality. |
| 00:39 | It provides many other important mathematical and scientific functions. |
| 00:43 | After running IPython -pylab in the shell, you will see some information about 'ipython' and pylab followed by the In[1] prompt. |
| 00:55 | But, if you get an error like 'ERROR: matplotlib could NOT be imported! Starting normal IPython.' |
| 01:02 | then you will have to install the matplotlib and run this command again. |
| 01:08 | Now type: 'linspace' followed by a '?' mark in your ipython shell. |
| 01:19 | As the documentation says, it "returns 'num' evenly spaced samples, calculated over the interval 'start' and 'stop'". |
| 01:29 | To illustrate this, let's try to generate 100 points. |
| 01:33 | Type: linspace within brackets 1 comma 100 comma 100 and hit Enter. |
| 01:47 | As you can see, a sequence of numbers from 1 to 100 appears. |
| 01:52 | Now let's try to generate 200 points between 0 and 1. |
| 01:57 | we do that by typing linspace within brackets 0 comma 1 comma 200. |
| 02:11 | Here, 0 is the start, 1- the stop and 200- the number of points. |
| 02:18 | In linspace, the start and stop points can be integers, decimals or constants. |
| 02:24 | Let's try and get 100 points between minus 'pi' to 'pi'. |
| 02:30 | Here 'pi' is a constant defined by pylab. |
| 02:34 | Save this to the variable, say 'p'. |
| 02:52 | If we now type 'len' within brackets 'p', we will get the no. of points. |
| 03:05 | len function gives the no. of elements of a sequence. |
| 03:11 | Let's try and plot a cosine curve between minus 'pi' and 'pi'. For this, we use the plot command. Here, cos(p) gets the 'cosine' value at every point corresponding to point 'p'. |
| 03:50 | We can save cos(p) to variable 'cosine' and then plot it using the plot function. |
| 03:57 | Now, to clear the plot, we use the clf closing brackets function. |
| 04:19 | This is done because, if we wish to make another plot, it will overlap the previous plot. |
| 04:25 | As we do not wish to clutter the area with overlaid plots, we just clear it with clf(). |
| 04:34 | Now, let's try a 'sine plot'. |
| 05:04 | We can study the plot better on the plot window by using the various options available on it. |
| 05:11 | Let us have a look at these options. |
| 05:14 | As we can observe, moving the mouse pointer along the plot gives us the location of each point on the plot. |
| 05:26 | To the bottom left of the window, there are a few buttons. |
| 05:30 | The right most among them is for saving the file. |
| 05:35 | Just click on it and type the file name. |
| 05:48 | We will save the file by the name 'sin_curve' in 'pdf' format. |
| 06:00 | As you can see, we can specify the format of file from the drop-down. |
| 06:05 | Formats like png, eps, pdf, ps are available. |
| 06:17 | Left to the save button is the slider button by which we can specify the margins. |
| 06:25 | Left to this is the zoom button by which we can zoom into the plot. |
| 06:30 | Just specify the region to zoom into. |
| 06:40 | The button to the left of it can be used to move the axes of the plot. |
| 06:50 | The next two buttons with left and right arrow icons change the state of the plot and take it to the previous state it was in. |
| 07:00 | It more or less acts like the back and forward button in a browser. |
| 07:06 | The last one is home, referring to the initial plot. |
| 07:13 | Pause the video here, try out the following exercise and resume the video. |
| 07:20 | Plot (sin(x) into sin(x)) by x. |
| 07:26 | 1. Save the plot by the sin square by x.pdf in pdf format. |
| 07:33 | Second one. Zoom and find the maxima. |
| 07:37 | 3. Bring it back to initial position. |
| 07:44 | Now, let's revise quickly what we have learnt today- |
| 07:49 | To Study Ipython with pylab. |
| 07:52 | To Use the linspace function to create num equally spaced points in a region. |
| 07:57 | To Find the length of sequences using len function. |
| 08:01 | Plot mathematical functions using plot. |
| 08:05 | To clear drawing area using clf. |
| 08:08 | To Use the UI of plot for studying it better and using functionality like save, zoom and moving the plots on x and y axis. |
| 08:23 | Create 100 equally spaced points between minus pi by 2 and pi by 2? |
| 08:31 | Second one is- How do you clear a figure in ipython? |
| 08:36 | The third one- How do you find the length of a sequence? |
| 08:43 | And the answers are- |
| 08:45 | 1. We use the command linspace within brackets 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. |
| 09:03 | Second one- We use clf closing bracket function to clear a figure. |
| 09:11 | Third one- len within brackets 'sequence_name' is the function used to find out the length of a sequence. |
| 09:20 | Hope you have enjoyed and found it useful. |
| 09:24 | Thank you! |
