Additive preservers of numerical range Original Research Article

We characterize all additive mappings preserving (classical) numerical range on various subalgebras of image : the subalgebra of all diagonal matrices image , the subalgebra of all (upper) triangular matrices image and subalgebras of block diagonal and block triangular matrices. Characterizations obtained show that in some cases, image for example, all such preservers are linear. On the other hand, we show that the group of all additive preservers on image contains some additional mappings.