# Tag Info

Accepted

### When do not use preconditioners for sparse linear system of equations?

In my experience, you always need (or better use) some form of preconditioning. The type and complexity of the precondition would vary depending on the task though. From Y. Saad, Iterative Methods for ...
• 8,382
Accepted

### Without positive definiteness, does an iterative solver work?

No, positive definiteness (and symmetry) are only precondition to using the Conjugate Gradient method. But there are plenty of other iterative methods such as MinRes and GMRES that can be used for ...
• 50.7k
Accepted

### Using matrix exponential to solve linear system

You are effectively asking how to compute $y=(\log M )^{-1}b$, where $M=e^A$ is the given matrix. There are several methods for computing $f(M)b$ without forming $f(M)$, and they are reviewed here. ...
• 956