[petsc-users] using fieldsplit for matrix assembled using aij

[Barry Smith]

  -pc_fieldsplit_block_size  3 (you may not need this if the code sets the block size to 3).

  -pc_fieldsplit_0_fields 0,1
  -pc_fieldsplit_1_fields 2





> On Jul 31, 2020, at 7:05 PM, Raju Mandhapati via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> Hello,
> 
> I have a matrix assembled in interlaced format. I am not able to follow how to use fieldsplit. Is there a good example to show how to do this.  My variable are in this format [ {u1,v1,p1}, {u2,v2,p2}, ....,{un,vn,pn}], where n is the number of grid points and u,v,p are the velocity and pressure components. The matrix is assembled as
> 
> [ uu11 uv11 up11  uu12 uv12 up12 ......
>   vu11 vv11 vp11  vu12 vv12 vp12 .......
>   pu11 pv11 pp11 pu12 pv12 pp12 ......
> 
>   uu21 uv21 up21  uu22 uv22 up22 ......
>   vu21 vv21 vp21  vu22 vv22 vp22 .......
>   pu21 pv21 pp21 pu22 pv22 pp22 ......
>   
>   .
>   .
>  
> ]
> 
> I want to split u and v fields as one block and p field as another block.
> 
> Any help would be appreciated.
> 
> Raju.
>  
>   
>