A linear system is a set of simultaneous linear equations treated together and often written in matrix form. The compact matrix form scales better than listing equations one by one, especially when many unknowns are involved. section 2.12
The basic goal is to find unknown values that make the matrix equation true. In the simple square, invertible case, the solution parallels the one-variable rule x = a−1b. section 2.12
Key behaviors of linear systems in this treatment:
- Square, invertible systems have an exact solution through matrix inverse. section 2.12
- Zero determinants make the system singular and unsolvable exactly. section 2.12.1
- Near-zero determinants make the system numerically unstable. section 2.12.1
- Non-square systems are handled with the Moore-Penrose pseudo-inverse or SVD-based methods. section 2.12.4 section 4.5.4
Toy training equations
A small machine learning example turns training data into equations such as 0.11w0 + 0.09w1 + b = −0.8 and similar rows for other samples. The same setup is also shown as a larger overdetermined system with many training examples. section 2.12 section 2.12.4
| a11x1 + a12x2 + a13x3 + … + a1nxn = b1 |
Shows the general n-equation, n-unknowns layout in explicit row form. section 2.12

