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# Introduction to matplotlib

## Olav Vahtras

Computational Python

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## Matplotlib

- The standard 2D-plotting library in Python
- Production-quality graphs
- Interactive and non-interactive use
- Many output formats
- Flexible and customizable

---

## First example

### The absolute minimum  you need to know

* You have a set of points (x,y) on file

```
-3.141593 -0.000000
-3.013364 -0.127877
-2.885136 -0.253655
...
3.141593 0.000000
```
--

* How do you get to  this

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### Next

* Import the plotting library
```python
import matplotlib.pyplot as plt
import numpy as np
```
--

* Load the data from file
```python
data = np.loadtxt('filename')
```
--

* Call the `plot` function
```
plt.plot(data[:, 0], data[:, 1])
```
--

* Show the result
```
plt.show()
```

*Note:* in ipython notebook you may want to do
```
%matplotlib inline
```
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### Next?

#### Refinement

* Change color, linestyle, linewidth
--

* Change window size (ylim)
--

* Change xticks
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* Set title
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* Multi-line plots
--

* Legends

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#### A more advanced example
```python
fig, ax1 = plt.subplots()
ax1.plot(orbital, dataset1, 'b-')
ax1.set_xlabel('orbital')
# Make the y-axis label and tick labels match the line color.
ax1.set_ylabel('occupied', color='b')
for tl in ax1.get_yticklabels():
    tl.set_color('b')
ax2 = ax1.twinx()
ax2.plot(orbital, dataset2, 'r-')
ax2.set_ylabel('virtual', color='r')
ax2.set_ylim(ax2.get_ylim()[::-1])
for tl in ax2.get_yticklabels():
    tl.set_color('r')
```
<img src="img/dualplot.png" height="325"/>

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### In practice

* How do you do when need a particlar type of figure?
--

* Go to the matplotlib gallery: http://matplotlib.org/gallery
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* Try some exercises at

http://scipy-lectures.github.io/intro/matplotlib/matplotlib.html#other-types-of-plots-examples-and-exercises

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