```
clear; clc; close all;
format default;
profile on;
```
visualize the nonzero elements of a matrix
```
spy()
```
matlab is column-major that explains so much
accessing column wise is much faster than row wise in Matlab
sparsity is the fraction of the matrix that are zeros
only use sparse matrices for matrices that are actually sparse enough for it to matter
Operations that preserve sparsity:
- addition
- subtraction
- element-wise multiplication
- kronecker multiplication
Operations that do NOT preserve sparsity
- algebraic multiplication
- inverse or pseudo-inverse
- eigen-decomposition, SVD
```
surf(X,Y,Z)
mesh(X, Y, Z);
contour
contourf
colorbar
view(2);
shading interp;
print('-dpng', '-r400', 'contour_plots');
savefig('contour_plots')
```
plot errors in log log scale
show how much time different functions are taking
```
profile on
% code here
profile viewer
```