What does the syntax;
<< X >>
mean? Where X is a number?
Cheers
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$\begingroup$ normally you will find this in the middle of a large list n your output. For example if you had 10000 elements in a list you might see the first 5 then <<990>> and then the last 5. The <<X>> indicates that there are X elements that exist but are not being shown in the output in order to limit the output size $\endgroup$ – Mike Honeychurch Jan 7 '16 at 3:44
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$\begingroup$ It's not syntax, it cannot be used in input at all. It means that X elements were not printed in the output. $\endgroup$ – Szabolcs Jan 7 '16 at 9:29
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$\begingroup$ Possibly of interest: (51543), (79231) $\endgroup$ – Mr.Wizard Jan 7 '16 at 12:58
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Directly from the Help Center:
When you generate a very large output expression in the Wolfram Language, you often do not want to see the whole expression at once. Rather, you would first like to get an idea of the general structure of the expression, and then, perhaps, go in and look at particular parts in more detail.
The functions Short and Shallow allow you to see "outlines" of large Wolfram Language expressions.
t = Expand[(1 + x + y)^12];
Short[t]
$$1+12 x+66 x^2+220 x^3+495 x^4+792 x^5+\langle\langle 80\rangle\rangle +132 x y^{10}+66 x^2 y^{10}+12 y^{11}+12 x y^{11}+y^{12}$$
...
When generated outputs in the notebook interface are exceedingly large, the Wolfram Language automatically applies Short to the output. This user interface enhancement prevents the Wolfram Language from spending a lot of time generating and formatting the printed output for an evaluation which probably generated output you did not expect.
lst = Range[10^6]
See also Textual Input and Output
