[petsc-users] VecAXPY

[José Lorenzo]

Hello,

I am struggling with a strange error when using VecAXPY. I have a ghost
vector H that needs to be updated as

H = H + eta * dH - eta_old * dH

However, for some reason I obtain different results when using

call VecAXPY(H, eta - eta_old, dH, ierr)

instead of

call VecAXPY(H, - eta_old, dH, ierr)

call VecAXPY(H, eta, dH, ierr)

where eta and eta_old are PetscScalars.

The first option seems to provide a wrong output, but I do not understand
what can go wrong in such simple operation.

Thank you.
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