WordSeparators is an option for Read, Find, and related functions that specifies the list of strings to be taken as delimiters for words.
ZeroTest is an option to various linear algebra functions that gives a function to use in testing whether symbolic expressions should be treated as zero.
$BatchOutput is True if output in the current session is being sent in batch mode, suitable for reading by other programs.
$ByteOrdering gives the native ordering of bytes in binary data on your computer system.
$KernelCount gives the number of subkernels available for parallel computations.
$NewSymbol is a global variable which, if set, is applied to the name and context of each new symbol that Mathematica creates.
$SyntaxHandler is a global variable which, if set, is applied to any input string that is found to contain a syntax error.
$SystemID is a short string that identifies the type of computer system on which Mathematica is being run.
Converting between strings, boxes, and expressions. Here is a simple expression. This gives the InputForm of the expression as a string.
The general form of a linear second-order PDE is Here uu(x,y), and a, b, c, d, e, f, and g are functions of x and y only—they do not depend on u. If g0, the equation is ...