[Pw_forum] Question on based-centered monoclinic cell input

[Yansun Yao]

Dear Pwscf users,
   I have a question on the input defining a based-centered monoclinic cell
(ibrav=13).  If I input the relevant information as described in the
documentation, I did not get the correct crystal matrix.  I inspect the routine
latgen.f90 and found that the program produce the fllow lattice which I do not
quite understand
   In unit of alat, the latgen routine generates

    cos(ab)   0    sin(ab)
    cos(ab)   0   -sin(ab)
      b/a    c/a    0
   For a based cnetered cell, I expect the two vectors on the
plane should be 1/2(a+b) and 1/2(a-b)?
   Is the program expected a different setting?  If so, what
is it?
   Any explanation and help is greatly appreciated. Thank you!
                                  Yansun 
                             University of Saskatechwan