3. Function graph as a manifold
This notebook is part of the Introduction to manifolds in SageMath by Andrzej Chrzeszczyk (Jan Kochanowski University of Kielce, Poland).
The graph
for a smooth function and an open subset is a simple example of a smooth manifold having an atlas with a single chart
One-dimensional function graph as a manifold
Since we don't use any predefined charts or transitions in this case, we can use general manifold (not the Euclidean space as previously).
Example 3.1
Here we use an open interval :
First we plot as a subset of defined as
And next the image of under sinus function as a subset of .
Example 3.2
Below, we map the same open interval into .
Two-dimensional function graph as a manifold
Example 3.3
Now let be an open rectangle in .
First we plot the coordinate lines in the set .
The graph of the function as a subset of :
Example 3.4
Now we show a similar example using polar coordinates. We need two charts in this example. If we don't use the Euclidean space, we need to define both Cartesian and polar coordinates and also the transition map
First we plot the coordinate lines :
And next the image of these lines as a subset of :
Three dimensional function graph as a manifold
Example 3.5
First we show the coordinate lines in the three dimensional rectangle:
And next the image under the map :
Example 3.6
Finally let us show 3-dimensional example in spherical coordinates.
First we show some coordinate lines of the open set defined by:
(the transition map must be defined by the user).
And next the image of these lines under the mapping which triples the coordinate.
What's next?
Take a look at the notebook Spheres as manifolds.