# Problem solving

SECTION UNDER CONSTRUCTION.

## Possible issues

- Modify
`sbound`

if isostaticity gap is negative for several steps due to`abs(s_i)=sbound*R`

- If isostaticity gap is too big (and positive), possibly there is small precision in the value of dual variables (
*e.g.*when using Tulip). This could be solved by looking for dual variable larger than a given threshold value, but still needs to be implemented.- This might be the case even when such gap is not too big. For instance, using GLPK in the LS tests, the initial iterations throw a gap of about +6 (due to very small forces)

- A
*negative*isostaticity can be caused by the maximal displacement (of*stable*particles) being equal to the bound on $|s_{i,\mu}^\star|$. If this happens, try using a larger value of`sbound`

.- In reality, what happens is that there is an
*active*dual variable related to such bound on the displacements and*not*to a contacts. Thus, the system is nonetheless isostatic, but a contact has not being properly counted, since it is not included in the lists of`constraints`

in the main loop.

- In reality, what happens is that there is an
- The right convergence tolerance values,
*i.e.*the right choice of`tol_Γ_convergence`

and`tol_S_convergence`

possibly depend on the solver `Tulip.jl`

give an isostatic config only when the status of the optimization is`ITERATION_LIMIT`

, which also entails that forces are determined with very, very low accuracy. Notably, even though this happens, the force mismatch is very small.

### Setting the required precision

## Overlaps occur

### Due to numerical error

### REAL overlaps

When this occurs, it is likely that the value of `sbound`

is too large with respect of the value of $\ell$ used. So try using a larger value of `ℓ0`

(if this occurred when $\Gamma^\star$ was still relatively large).

- Try using a smaller value of
`sbound`

. - Or try redefining the bounds with which $\ell$ is adjusted as CALiPPSO makes progress.
- These three options can be set as keywords arguments of
`produce_jammed_configuration!`

as explained in this section. - See the docstring of
`bounds_and_cutoff`

for more info.