[Dune] Error in implementing PAAMG using dune-istl

[Christian Engwer]

On Thu, Dec 14, 2017 at 01:46:04PM +0100, Kumar, Paras wrote:
> Dear Christian,
> 
> Thank you for the email.
> 
> 1. The problem tested is Ax=b where the matrix A comes form a FE
> discretization of the laplacian in 1d and is thus a tridiagonal matrix. The
> right hand side b has been taken such that the exact solution is x=1.0

My question did not refer to the test problem, but to "what did you
try to find the bug?".

> 2. The segfault happens at line 486 of the previously attached code file.

No, it does not happen at line 486. Line 486 is a call to the amg
constructor. This does not help you at all inderstanding what goes
wrong.

What you should do/answer/ask yourself
a) compile with debug symbols enabled
b) run the program under a debugger
c) check which is the last call in Dune land
d) which variable is accessed
e) what is the state of this variable
f) guessing from you error message the problemis an out-of-bounds
   access in a matrix row
g) if (f) is true: is this matrix row really properly filled?

Best
Christian