Magnetic structure of the noncentrosymmetric perovskites<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="bold">PbVO</mml:mi><mml:mn mathvariant="bold">3</mml:mn></mml:msub></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="bold">BiCoO</mml:mi><mml:mn mathvariant="bold">3</mml:mn></mml:msub></mml:math>: Theoretical analysis