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`_.`Indeterminate Noun

Indeterminate (`_.`) is a numeric atom.
It is a placeholder broadly comparable with NaN (not a number).
See: WikiPedia:NaN
and Essays/Indeterminate.

It can appear in data imported from external sources, eg from a DLL or data base package. For an exhaustive list of sources see the entry in the J Dictionary.

If a computation produces NaN when the arguments were not NaN, J will signal a `NaN error`. If a NaN is an argument to a computation, it is undefined what the result value is: it could be NaN or any other value.

Some computations that produce NaN according to the IEEE standard do not produce NaN in J:

`0 * _ = 0``0 * __ = 0``0 % 0 = 0``0 ^ 0 = 1``_ ^ 0 = 1``1 ^ _ = 1`

p=: _ [ q=: __ p+q |NaN error | p +q p%q |NaN error | p %q 0*p,q 0 0 1%q 0

### Common uses

**Indeterminate** (`_.`) is **not recommended for use** in J computations.
It signifies a "missing value" in statistical data.
You should detect it using `128!:5` and replace it at the first opportunity with a proper numeric value suited to the computation you want to perform, eg (`0`), (`_`) or (`__`).

z 1 2 _. 4 128!:5 z 0 0 1 0 0 (I. 128!:5 z) } z NB. replace missing values with ZERO 1 2 0 4

### More Information

**Indeterminate** is the only numeric atom that is **not equal to itself**. Further bizarre properties arise from this fact.

See Essays/Indeterminate.

z=: 1 2 _. 4 1+z 2 3 _. 5 z=z 1 1 0 1 +/z _.

Numbers (`".`) can take a left argument.
This specifies a numeric atom to replace any ill-formed numbers.
This (together with `3!:n`) are the only ways to force `_.` to arise in pure-J code.
**But it is not recommended for the purpose!** Use (`0`) or Infinity (`_`) instead.

z=: '.2 0.2 2.45 3E56 3F56 _1 _0 77' NB. (".) accepts non-J-numerals like '.2' and '3E56' but not '3F56' ... ".z |ill-formed number | ".z _. ".z 0.2 0.2 2.45 3e56 _. _1 0 77 0 ".z NB. replace bad-numerals by ZERO 0.2 0.2 2.45 3e56 0 _1 0 77 _ ".z NB. replace bad-numerals by INFINITY 0.2 0.2 2.45 3e56 _ _1 0 77