fixes #3451

Author: mahrud

M2/Macaulay2/m2/genmat.m2

@@ -72,6 +72,7 @@ random(List,Ring) := RingElement => opts -> (deg,R) -> (
 
 random(ZZ,Ring) := RingElement => opts -> (n,R) -> random({n},R,opts)
 
+other := (i, m) -> (i + random m) % m
 randomMR := opts -> (F,G) -> (
      R := ring F;
      m := numgens F;
@@ -83,7 +84,6 @@ randomMR := opts -> (F,G) -> (
      if m>k then f = f || random(R^(toList( m-k : d1 )), R^n, opts)
      else if n > k then f = f | random(R^m, R^(toList (n-k : -d1)), opts);
      f = mutableMatrix f;
-     other := (i,m) -> (i + random(m-1)) % m;
      if m>k then (
 	  for i to k-1 do rowAdd(f, i, random(d0,R,opts), random(k,m-1));
 	  for i to k-1 do rowSwap(f, i, other(i,m)))

M2/Macaulay2/tests/normal/randommat.m2

@@ -31,3 +31,6 @@ assert isIsomorphism random(R^4,R^4,MaximalRank=>true)
 assert isInjective random(R^6,R^3,MaximalRank=>true)
 assert isSurjective random(R^3,R^6,MaximalRank=>true)
 
+assert(random(ZZ^2, ZZ^2, MaximalRank => true) - id_(ZZ^2) != 0)
+assert(random(QQ^2, QQ^2, MaximalRank => true) - id_(QQ^2) != 0)
+assert(random(R^2,  R^2,  MaximalRank => true) - id_(R^2)  != 0)