System Variables

System variables are names beginning with ⎕ (quad). They control interpreter behaviour.

⎕IO — Index Origin

Default	1
Valid values	0 or 1

Controls where counting starts. Affects ⍳ (iota), ⍋ ⍒ (grade), ⌷ (From), bracket indexing, and dyadic ⍳ (index-of).

      ⎕IO
1
      ⍳5
1 2 3 4 5
      ⎕IO←0
      ⍳5
0 1 2 3 4

⎕CT — Comparison Tolerance

Default	1E¯14
Valid values	Any non-negative number

Controls tolerant comparison for floating-point numbers. Two values a and b are considered equal if |a-b| ≤ ⎕CT × (|a| ⌈ |b|).

Affects: = ≠ < ≤ ≥ >, dyadic ⍳ (index-of), ∈ (membership).

Does not affect: ≡ (match) and ≢ (not-match), which always use exact comparison.

      1=(1÷3)×3          ⍝ tolerant: floating-point 0.999... equals 1
1
      ⎕CT←0              ⍝ exact comparison
      1=1.001
0

Set ⎕CT←0 when you need exact floating-point comparison.

Note

⎕PP (print precision) is not a settable system variable. Display precision is fixed at 10 significant digits.