[petsc-users] a line of code is weird

[Fande Kong]

Hi all,

I am trying to understand how to compute Jacobian using finite difference
methods. There is a function called SNESComputeJacobianDefault, where a
line of code at 120th
line, MatSetValues(B,1,&j,1,&i,y+j-start,INSERT_VALUES), is difficult to
understand for me. Because I think inserting  'y' is enough, but there is
two extra values 'j-start'. Any explanation is welcome.

Thanks,

Fande,
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