trace

trace f -- returns the trace of the matrix f.

     i1 = R = ZZ/101[a..d]
     
     o1 = R
     
     o1 : PolynomialRing

     i2 = p = matrix {{a,b},{c,d}}
     
     o2 = | a b |
          | c d |
     
                  2       2
     o2 : Matrix R  <--- R

     i3 = trace p
     
     o3 = a + d
     
     o3 : R