Undefined values: Difference between revisions

Mathematica is a symbolic mathematical software. Variables without given values are treated as symbols.

<lang Mathematica>a

-> a

a + a

-> 2 a

ValueQ[a]

-> False

a = 5

-> 5

ValueQ[a]

-> True</lang>

Mathematica also has a build-in symbol "Undefined", representing a quantity with no defined value.

<lang Mathematica>ConditionalExpression[a, False]

->Undefined</lang>

<lang Mathematica>Sin[Undefined]

Of course you can assign Undefined to be the value of a variable. Here "Undefined" is itself a value.

<lang Mathematica>a = Undefined

-> Undefined

a

-> Undefined

ValueQ[a]

-> True</lang>