Hi,
I looked into the ¯4○ thing a bit more and have identified the discrepancy
between APL2 and GNU APL, which may or not be a bug depending on whether
the ISO spec agrees with APL2 on this function.
According to the APL2 language reference, if the real part is greater than
or equal to zero, or the real part is between -1 and zero with the
imaginary part zero, you return (¯1+X×X)*0.5. Otherwise you flip the sign
and return -(¯1+X×X)*0.5.
So in APL2....
8 1⍴¯4○1D45*-⎕IO-⍳8
0.000000000E0
4.550898606E¯1J 1.098684113E0
7.146297292E¯16J 1.414213562E0
¯4.550898606E¯1J 1.098684113E0
¯3.814090016E¯8J 3.814090016E¯8
¯4.550898606E¯1J¯1.098684113E0
¯1.342666713E¯15J¯1.414213562E0
4.550898606E¯1J¯1.098684113E0
and in GNU APL
8 1⍴¯4○1D45*-⎕IO-⍳8
0
4.550898606E¯1J1.098684113E0
0J1.414213562E0
4.550898606E¯1J¯1.098684113E0
1.10663761E¯8J¯1.10663761E¯8
4.550898606E¯1J1.098684113E0
0J1.414213562E0
4.550898606E¯1J¯1.098684113E0
As you can see, APL2 flips the signs on half the values, and GNU APL does
not.
So APL2 cancels, and GNU APL adds up to a big value when you sum them.
So that's why they are different.
Whether this is "wrong" remains to be seen, but it's a case where APL2 and
GNU APL do things differently.
On Sun, Aug 30, 2015 at 9:37 PM, Mike Duvos <m...@wolf359.net> wrote:
> Dropped an iota in the prior post.
>
> X←1D1*⍳360
> +/¯4○X
> ¯3.814090113E¯8J3.814086508E¯8
>
> That changes the IBM result slightly, but the GNU APL one is still off by
> a large amount.
>
>
>
> On Sun, Aug 30, 2015 at 9:13 PM, Mike Duvos <m...@wolf359.net> wrote:
>
>> )CLEAR
>> CLEAR WS
>> ⎕IO←0
>> X←1D1*360
>> +/(¯1+X×X)*0.5
>> 5.393937829E¯8J¯5.393937829E¯8
>>
>> [IBM APL2]
>>
>> +/¯4○X
>> 5.393937829E¯8J¯5.393937829E¯8
>>
>> [GNU APL]
>>
>> +/¯4○X
>> 122.0040743J2.828427087
>>
>> I think this is wrong.
>>
>>
>>
>
