Hi,

I try to use BandedMatrices package and I can’t set values in the symmetric case:

```
using BandedMatrices
a=BandedMatrix{Float64}(10,1,1)
fill!(a,0.0) #OK
BandedMatrices.inbands_setindex!(a,12.0,1,2) #OK
b=SymBandedMatrix{Float64}(10,1)
fill!(b,0.0) #KO indexing not defined
BandedMatrices.inbands_setindex!(b,12.0,1,2) #KO indexing not defined
```

The documentation does not say much about symmetric matrices so I start to read the implementation but it is not trivial to me…

What would be the correct way to set values in symmetric banded matrices

Thank you for your help.

Laurent