# ⎕IC - Indeterminate Control

 Z←⎕IC returns the current value of the Indeterminate Control vector.
Z is an integer vector whose elements each control a separate aspect of how indeterminates are handled by the system.

 ⎕IC←R sets all of the values of the Indeterminate Control Vector to R. ⎕IC←⍬ sets all of the values of the Indeterminate Control vector to their system default state. ⎕IC[L]←R sets the value(s) of the Indeterminate Control vector indexed by L to R.

This experimental feature attempts to collect together in one place control of various infinite and indeterminate calculations such as ÷0, 0÷0, and friends. The values of this multi-element vector each control a different calculation. In particular,

⎕IC Index
(origin-0)
Indeterminate
or Infinite Calculation
Default
Result
0 ÷0 or L÷0 for L≠0
1 ⍟0 ¯∞
2 !R for integer R<0 DOMAIN ERROR
3 0×∞ or ∞×0 DOMAIN ERROR
4 0×¯∞ or ¯∞×0 DOMAIN ERROR
5 0÷0 1
6 ∞÷∞ (same sign) DOMAIN ERROR
7 ∞÷∞ (different sign) DOMAIN ERROR
8 ∞-∞ (same sign) DOMAIN ERROR
9 L|∞ for L>0 DOMAIN ERROR
10 L|¯∞ for L>0 DOMAIN ERROR
11 L|∞ for L<0 DOMAIN ERROR
12 L|¯∞ for L<0 DOMAIN ERROR
13 ¯∞|R for R>0 ¯∞
14 ∞|R for R<0
15 0*0 1
16 L*∞ for L≤¯1 DOMAIN ERROR
17 0*∞ 0
18 0*¯∞
19 ±∞*0 DOMAIN ERROR
20 L*R for L<0 and non-integer R DOMAIN ERROR
21 0⍟0 1
22 0⍟1 DOMAIN ERROR
23 1⍟0 DOMAIN ERROR
24 1⍟1 1
25 0∨±∞ or ±∞∨0 LEFT
26 0∧±∞ or ±∞∧0 DOMAIN ERROR
27 0⍟R for R≠0 1 DOMAIN ERROR
28 L*¯∞ for ¯1 ≤ L < 0 DOMAIN ERROR

The values in each element of ⎕IC control the result of the calculation as follows:

⎕IC Value Result
¯1 ¯1
0 0
1 1
2 DOMAIN ERROR
3
4 ¯∞
5 NaN (∅)
6 LEFT
7 RIGHT

For example,

```      ⎕IO←0
⎕IC
3 4 3 2 2 1 2 2 2 2 2 2 2 4 3 1 2 0 3 2 2 1 2 2 1 5 2 2 2
0÷0
1
⎕IC[5]←2
⎕IC
3 4 3 2 2 2 2 2 2 2 2 2 2 4 3 1 2 0 3 2 2 1 2 2 1 5 2 2 2
0÷0
DOMAIN ERROR
0÷0
∧
⎕IC←⍬
⎕IC
3 4 3 2 2 1 2 2 2 2 2 2 2 4 3 1 2 0 3 2 2 1 2 2 1 5 2 2 2
```

To set all indeterminate results to DOMAIN ERROR, use ⎕IC[]←2.

## Incomplete List of Indeterminates

There may be other indeterminates not covered by this feature. Please let us know if you think there are other cases that should be included.

System Variables (A value may be assigned to these except for ⎕DM)
ALX CT DM DT ELX FC FEATURE FPC IC IO
LR LX PP PR PW RL SA WSID
Niladic System Functions (a value cannot be assigned to these)
A AV EM ET LC NNAMES NNUMS SI SYSID SYSVER
T TC TCBEL TCBS TCESC TCFF TCHT TCLF TCNL TCNUL
TS WA
Monadic or dyadic system functions (a value cannot be assigned to these)
AT CR DC DFT DL DR EA EC ERROR ES
EX FMT FX MF NAPPEND NC NCREATE NERASE NINFO NL
NLOCK NREAD NRENAME NREPLACE NRESIZE NSIZE NTIE NUNTIE STOP TF
TRACE UCS VR
Note that quad functions and variables (except for the ⎕A family of functions) are case insensitive

 See Also System Commands System Variables and Functions Operators

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