map(Module,Module,RingElement)

map(M,N,r) -- construct a map from a module N to M which provided by the ring element r.

If r is nonzero, then M and N should be equal, or differ at most by a degree (i.e., by tensoring with a graded free module of rank 1).

     i1 = R = ZZ/101[x]
     
     o1 = R
     
     o1 : PolynomialRing

     i2 = map(R^2,R^3,0)
     
     o2 = 0
     
                  2       3
     o2 : Matrix R  <--- R

     i3 = map(R^2,R^2,x)
     
     o3 = | x 0 |
          | 0 x |
     
                  2       2
     o3 : Matrix R  <--- R

     i4 = q = map(R^2,R^2,x,Degree=>1)
     
     o4 = | x 0 |
          | 0 x |
     
                  2       2
     o4 : Matrix R  <--- R

     i5 = isHomogeneous q
     
     o5 = true