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Matlab usage - short (may be too short) introduction
%!style(html): ../evmik.css
= How to make a simple plot =
Suppose during the measurements we obtain the following data
fir each parameter 'I' we measured 'V' with a particular uncertainty dV.
Our data is represented in the following table.
|| I | V | dV |
| .1 | 1.0 | 0.2 |
| 1.0 | 2.2 | 0.1 |
| 1.8 | 3.2 | 0.2 |
| 3.3 | 3.8 | 0.2 |
| 4.0 | 4.9 | 0.3 |
First of all, we need to transfer it to the Matlab vector variables. Pay
attention to the delimiter **;** between numbers
```
I = [ .1; 1.0; 1.8; 3.3; 4.0 ]
V = [ 1.0; 2.2; 3.2; 3.8; 4.9 ]
dV = [ 0.2; 0.1; 0.2; 0.2; 0.3 ]
```
Now we make a simple plot without error bars to get the basic, text after
**%** is considered as a comment and matlab will disregard it.
```
figure(1) % all plotting output will go to the particular window
plot(I,V)
```
Easy, is not it?
[simple_labeled_plot.png]
But **every plot must be present with title, proper axes labels and units**.
Note **'** for the string specifiers
No our plot is nice and pretty.
[simple_unlabeled_plot.png]
= Fixing the range of the axes =
Have a look at above plot. We see that one of the axes (y) does not contain
origin point (y=0). Such plots are very common in finances and design to
fool a reader, but they are generally not acceptable in scientific reports
and definitely not in my class unless you have a good reason to do
otherwise.
The fix is very easy. Note that we are actually sending a vector [0,5] to the
**``ylim``** function (fir x-axis we need to use **``xlim``** function).
``` ylim([0,5])
Now our plot is good to present
[simple_labeled_and_proper_limits_plot.png]
= Plotting with error bars =
Let's open a new window for the plot
``` figure(2)
Now we make plot with error bars assuming that they are the same for up and down parts
``` errorbar(I,V,dV)
Yet again we need proper labeling
```
title('Dependence of voltage on current')
xlabel('Voltage (V)')
ylabel('Current (A)')
```
[errorbar_plot.png]
= Fixing plots font size =
Honestly Matlab is not the best tool to do presentation quality plots, it requires a quite a bit of messing with their GUI. But at least for quick font size fix do the following. This looks a bit like magic spell.
```
fontSize=24;
set(gca,'FontSize',fontSize );
errorbar(I,V,dV)
title('Dependence of voltage on current')
xlabel('Voltage (V)')
ylabel('Current (A)')
```
[errorbar_with_large_font_plot.png]
= Saving you matlab plots =
Well it nice to have matlab plots. But as soon as you close matlab they will go away.
How to save them for a future use? Actually, quite easy.
For png output do
``` print('V_vs_I.png')
or if you need a pdf (matlab usually make very bad pdfs)
``` print('V_vs_I.pdf')
Make sure that you read documentation for **``print``** command there are some useful parameters.
|
