  In the Density Matrix Renormalization Group (DMRG), multiple states must be
included in the density matrix when properties beyond ground state are needed,
including temperature dependence, time evolution, and frequency-resolved
response functions. How to include these states in the density matrix has been
shown in the past. But it is advantageous to replace the density matrix by a
singular value decomposition (SVD) instead, because of improved performance,
and because it enables multiple targeting in the matrix product state
description of the DMRG. This paper shows how to target multiple states using
the SVD; it analyzes the implication of local symmetries, and discusses typical
performance improvements using the example of the Hubbard model's
photo-emission spectra on a ladder geometry.
