That is a very old bug! Can you make an MR to just call PetscPowScalar in a loop here https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/vec/vec/utils/projection.c*L1022__;Iw!!G_uCfscf7eWS!bbSdSMnU5KpH03jHI7aV5j4WLGQ3yPvxWzR6Lwr14QLy_7EJ2MNT-qhL6J1x6z3vpF6M5GQk9lMQkMoLJ_JNSn1mqwqict4$ ?
Thanks Il giorno gio 14 nov 2024 alle ore 17:39 Peder Jørgensgaard Olesen via petsc-users <petsc-users@mcs.anl.gov> ha scritto: > Given a vector containing roots of unity, v[i] = exp(i*k*x[i]) I wanted to > compute the vector u[i]=exp(i*n*k*x[i]), for some real number n. From the > face of it this should be easily achieved with VecPow, as u[i] = v[i]^n. > > That didn't work as expected, though I got around it using VecGetArray() > and a loop with PetscPowComplex(). The source designated in the docs > (src/vec/vec/utils/projection.c) reveals that VecPow() maps v[i] to > PETSC_INFINITY when the PetscRealPart(v[i]) < 0, unless the power is any of > 0, ±0.5, ±1 or ±2. Even in the simple case of a purely real vector (with > negative entries) raised to any other integer power, the results would not > be what one might reasonably expect from the description of VecPow(). > > While I do have a solution suiting my need, I'm left wondering what might > be the rationale for VecPow working the way it does. > > Best, > Peder > -- Stefano
