System Variable FEATURE - Revision history

WikiSysop at 20:40, 12 January 2023

2023-01-12T20:40:58Z

← Older revision		Revision as of 16:40, 12 January 2023
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	</pre></apll>		</pre></apll>

	Because <apll>¯0</apll> can not stored as a 64-bit Integer, this feature has a drawback of occasionally forcing a type promotion from Integer to Floating Point. For example, if <apll>R</apll> is an Integer array with <apll>0∊R</apll>, then an expression such as <apll>-R</apll> can no longer be stored as an Integer array, and must be promoted to Floating Point.		Because <apll>¯0</apll> can not be stored as a 64-bit Integer, enabling this feature has a drawback of occasionally forcing a type promotion from Integer to Floating Point. For example, if <apll>R</apll> is an Integer array with <apll>0∊R</apll>, then an expression such as <apll>-R</apll> can no longer be stored as an Integer array, and the entire array must be promoted to Floating Point, possibly losing precision because 64-bit Integers have <apll>63</apll> bits of precision and 64-bit Floating Point numbers have only <apll>53</apll>.<br />
	<br /></li>
			For example,<apll><pre>
			⎕FEATURE[2]←0
			0 ⎕DR ⎕←-¯1 0 1,⌊2*62
			1 0 ¯1 ¯4611686018427387904
			Integer (6412): 64 bits per element
			⎕FEATURE[2]←1
			0 ⎕DR ⎕←-¯1 0 1,⌊2*62
			1 ¯0 ¯1 ¯4.611686018427388E18
			Floating Point (6413): 64 bits per element</pre></apll>
			</li>

	<li>With the third feature disabled and then enabled:		<li>With the third feature disabled and then enabled:

WikiSysop at 21:54, 19 August 2019

2019-08-19T21:54:09Z

← Older revision		Revision as of 17:54, 19 August 2019
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	\|\|<apll>[3]</apll> \|\| User Hurwitz's Floor function instead of McDonnell's		\|\|<apll>[3]</apll> \|\| User Hurwitz's Floor function instead of McDonnell's
	\|-		\|-
	\|\|<apll>[4]</apll> \|\| ~~Allow~~ NaNs ~~(NaN = Not-a-Number~~)		\|\|<apll>[4]</apll> \|\| '''Withdrawn''' (formerly used to allow NaNs)
	\|-		\|-
	\|\|<apll>[5]</apll> \|\| Use APL2's definition of Inner Product		\|\|<apll>[5]</apll> \|\| Use APL2's definition of Inner Product
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	For more details on this topic, see [http://www.sudleyplace.com/APL/Hypercomplex%20GCD%20in%20APL.pdf Hypercomplex GCD in APL].<br /><br /></li>		For more details on this topic, see [http://www.sudleyplace.com/APL/Hypercomplex%20GCD%20in%20APL.pdf Hypercomplex GCD in APL].<br /><br /></li>

	<li>~~With the~~ fourth feature ~~disabled and then enabled:~~		<li>The fourth feature has been withdrawn.</li>

	~~<apll><pre>~~
	~~⎕FEATURE[4]←0~~
	~~0*0<hc>J</hc>1~~
	~~DOMAIN ERROR~~
	~~0*0<hc>J</hc>1~~
	∧
	~~⎕FEATURE[4]←1~~
	~~0*0<hc>J</hc>1~~
	~~∅<hc>J</hc>∅</pre></apll>~~

	~~A NaN is a special value supported by Fixed- and Multiple-precision arithmetic "representing an undefined or unrepresentable value, especially in floating-point calculations~~. Systematic use of NaNs was introduced by the [https://en.wikipedia.org/wiki/IEEE_floating_point IEEE 754] floating-point standard in 1985, along with the representation of other non-finite quantities like infinities"<sup>1</sup>.

	~~<br />~~</li>

	<li>With the fifth feature disabled and then enabled:		<li>With the fifth feature disabled and then enabled:
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	<br /></li>		<br /></li>
	</ul>		</ul>

	~~<h2>References</h2>~~

	~~<sup>1</sup> [https://en.wikipedia.org/wiki/NaN Wikipedia NaN]~~

	{{System Variables}}		{{System Variables}}
	{{Article footer}}		{{Article footer}}
	{{stub}}		{{stub}}

Sudleyplace at 10:04, 2 August 2018

2018-08-02T10:04:08Z

@@ Line 25: / Line 25: @@
 ||<apll>[4]</apll> || Allow NaNs (NaN = Not-a-Number)
 |-
 |}
@@ Line 104: / Line 105: @@
 A NaN is a special value supported by Fixed- and Multiple-precision arithmetic "representing an undefined or unrepresentable value, especially in floating-point calculations.  Systematic use of NaNs was introduced by the [https://en.wikipedia.org/wiki/IEEE_floating_point IEEE 754] floating-point standard in 1985, along with the representation of other non-finite quantities like infinities"<sup>1</sup>.
 <br /></li>
 </ul>

Sudleyplace at 15:08, 17 April 2018

2018-04-17T15:08:12Z

← Older revision		Revision as of 11:08, 17 April 2018
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	\| valign="top" \|<apll>⎕FEAURE←⍬</apll> \|\| sets all of the values of the Feature Control vector to their system default state.		\| valign="top" \|<apll>⎕FEAURE←⍬</apll> \|\| sets all of the values of the Feature Control vector to their system default state.
	\|-		\|-
	\|\| <apll>⎕FEATURE[L]←R</apll> \|\| sets the value(s) of the Feature Control vector indexed by <apll>L</apll> to <apll>R</apll> — ~~set~~ <apll>R</apll> to <apll>1</apll> ~~to enable~~ the feature, <apll>0</apll> ~~to disable~~ it.		\|\| <apll>⎕FEATURE[L]←R</apll> \|\| sets the value(s) of the Feature Control vector indexed by <apll>L</apll> to <apll>R</apll> — a <apll>1</apll> in <apll>R</apll> enables the feature, <apll>0</apll> disables it.
	\|-		\|-
	\|}		\|}
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	</pre></apll>		</pre></apll>

	When enabled, the first feature affects all contexts sensitive to the Index Origin.<br /><br /></li>		When enabled, the first feature affects all contexts sensitive to the Index Origin, such as the <apll>L</apll> in   <apll>R[L]</apll>,   <apll>R[L]←A</apll>,   <apll>R[L]f←A</apll>,   <apll>L⌷R</apll>,   <apll>L⍉R</apll>,   and   <apll>L⊃R</apll>.<br /><br /></li>

	<li>With the second feature disabled and then enabled:		<li>With the second feature disabled and then enabled:
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	÷÷∞ ¯∞		÷÷∞ ¯∞
	∞ ¯∞		∞ ¯∞
	</pre></apll><br /></li>		</pre></apll>

			Because <apll>¯0</apll> can not stored as a 64-bit Integer, this feature has a drawback of occasionally forcing a type promotion from Integer to Floating Point. For example, if <apll>R</apll> is an Integer array with <apll>0∊R</apll>, then an expression such as <apll>-R</apll> can no longer be stored as an Integer array, and must be promoted to Floating Point.
			<br /></li>

	<li>With the third feature disabled and then enabled:		<li>With the third feature disabled and then enabled:
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	</pre></apll>		</pre></apll>

	On the ~~other hand~~, McDonnell's Floor function isn't defined on Quaternions, but Hurwitz's is:		The industry standard definition of the Floor function on Complex numbers is McDonnell's. However, McDonnell's Floor function isn't defined on Quaternions, but Hurwitz's is:

	<apll><pre>		<apll><pre>
	a←<⍳4		a←<1 3 5 7÷2
	⎕FEATURE[3]←0 ⋄ ⌊a		⎕FEATURE[3]←0 ⋄ ⌊a
	DOMAIN ERROR		DOMAIN ERROR
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	∧		∧
	⎕FEATURE[3]←1 ⋄ ⌊a		⎕FEATURE[3]←1 ⋄ ⌊a
	1<hc>i</hc>2<hc>j</hc>3<hc>k</hc>4</pre></apll>		0<hc>i</hc>1<hc>j</hc>2<hc>k</hc>3</pre></apll>

			The two Floor functions return the same result for all Real numbers; they differ only on certain Complex numbers.

	The setting of this feature affects not only the result of the Floor function but also all other primitive functions directly or		The setting of this feature affects not only the result of the Floor function but also all other primitive functions directly or
	indirectly sensitive to the Floor function including Ceiling, Residue, Greatest Common Divisor, and Least Common Multiple.		indirectly sensitive to the Floor function including Ceiling (<apll>⌈R</apll>), Residue (<apll>L\|R</apll>), Greatest Common Divisor (<apll>L∨R</apll>), and Least Common Multiple (<apll>L∧R</apll>).

	For more details on this topic, see [http://www.sudleyplace.com/APL/Hypercomplex%20GCD%20in%20APL.pdf Hypercomplex GCD in APL].<br /><br /></li>		For more details on this topic, see [http://www.sudleyplace.com/APL/Hypercomplex%20GCD%20in%20APL.pdf Hypercomplex GCD in APL].<br /><br /></li>

WikiSysop at 20:59, 16 April 2018

2018-04-16T20:59:41Z

@@ Line 1: / Line 1: @@
-<h1>{quad}FEATURE - DEFINITION NEEDED</h1>
+<h1><aplxx>⎕FEATURE</aplxx> - Feature Control</h1>
-{{BoxStart|⎕FEATURE
+{{BoxStart|<apll>Z←⎕FEATURE</apll>
-| DEFINITION NEEDED}}
+| returns the current value of the Feature Control vector}}
-{{BoxEnd|⎕FEATURE←'<i>VALUE</i>'}}
+{{BoxEnd|<apll>Z</apll> is an integer vector whose elements each control a separate experimental Feature of the system.}}
-Description here - to do
 {{System Variables}}
 {{Article footer}}
 {{stub}}

Paul Robinson: new stub

2014-11-26T10:18:02Z

new stub

New page

<h1>{quad}FEATURE - DEFINITION NEEDED</h1>
{{BoxStart|⎕FEATURE
| DEFINITION NEEDED}}
{{BoxEnd|⎕FEATURE←'<i>VALUE</i>'}}

Description here - to do

{{System Variables}}
{{Article footer}}
{{stub}}