What's the meaning of <<19>> in the result [duplicate]

Question

Try the following:

Ty1 = {11, 13, 19, 22, 27, 30, 41};
Tm1 = {0.4125, 0.42, 0.4933, 0.525, 0.539, 0.575, 0.52};
Tx2 = {20, 18, 35, 37, 38, 44, 57};
Tm2 = {0.5625, 0.47, 0.58, 0.59, 0.57, 0.6, 0.58};
Tx3 = {9, 12, 19, 21, 24, 27, 32};
Tm3 = {1.044, 1.234, 0.874, 0.811, 0.82, 0.708, 0.828};
data = Table[{Tx2[[i]], Tm1[[i]], Tx2[[i]], Tm2[[i]], Tx3[[i]], 
    Tm3[[i]], Ty1[[i]]}, {i, 7}];
nlm = NonlinearModelFit[data, 
  k1*x2*m1^a + k2*x2*m2^b + k3*x3*m3^c + d, {k1, k2, k3, a, b, c, 
   d}, {x1, m1, x2, m2, x3, m3}, MaxIterations -> Infinity]

As output, you will get something like this

What is the meaning of <<18>> or <<19>>,and how to handle it?

Answer 1

The <<..>> notation in the output is called Skeleton and you don't have to handle it in any way, because the true expression is still there. Mathematica decided that the output would be too long for you to read and shortened it in a meaningful way.

The number that is used, like <<19>> tells you that there are 19 expressions hidden in this place. You can easily try this yourself, because Short or Shallow will produce them too:

Range[100]//Shallow
(* {1,2,3,4,5,6,7,8,9,10,<<90>>} *)

As you see, Mathematica hides 90 elements from the list. Nevertheless, you can still work with your computed result

Total[%]
(* 5050 *)