error in "xtimes" dfun in dfns.dyalog.com (Complex.numbers)

[Stu]

Has anyone tried using "xtimes"? The code is extremely compact and aesthetically pleasing, but the examples given produce this error:

RANK ERROR: Invalid axis
floop[0] floop←{(⊣/⍺)∇⍣(×m)⊢(+⌿⍵),[m-0.5]⍺×[⍳m←≢⍴⍺]-⌿⍵}

Did anyone encounter this, and, if so, were you able to fix it?

[JohnS|Dyalog]

Hi Stu,
Which example goes wrong?
You can see more examples in the test script: http://dfns.dyalog.com/s_xtimes.htm
John

[Stu]

I tried this example because I was mainly interested in just the FFT and iFFT:
x
9 3 5 8 1 0 5
y
6 2 3 7 4

iFFT (FFT 16↑x) × (FFT 16↑y)
54J¯9.32587E¯15 36J¯3.51108E¯15 63J¯6.38378E¯15 ...

floop seems to be the problem. I assumed I could take the definitions of FFT and iFFT out of the definition of xtimes and use them independently.

[JohnS|Dyalog]

I think the code is assuming an index origin of 0. Try:

      ⎕IO ← 0

[Stu]

⎕IO←0 did the trick, so now I can use FFT and iFFT. Cool!

I tried a couple of examples from the webpage you sent me to. I get "VALUE ERROR" on the final expression here:

x←¯50+?23⍴100
y←¯50+?17⍴100
(¯1+(⍴x)+⍴y)≡⍴x rconvolve y ⍝ OK
(x rconvolve y)≡x rconvolve⍨y ⍝ OK
(x convolve y)≡⌊0.5+9○x rconvolve y ⍝ PRODUCES VALUE ERROR

[JohnS|Dyalog]

I can't see anything wrong with your last line - and if I copy/paste it into my session, it works. Could you copy the output from a whole session, from starting up Dyalog - to getting the VALUE ERROR into an email please and send it to support at dyalog dot com? A bit like this:

      Dyalog APL/W Version 15.0.27638
Serial No : 000000
Unicode Edition
Thu Jul  7 10:13:52 2016
clear ws
      )load dfns
C:\15.0.dss\svn\misc\ws\unicode\dfns.dws saved Wed Jul  6 17:51:28 2016
                                                     
An assortment of D Functions and Operators (unicode).
                                                     
      tree #                ⍝ Workspace map.         
      ↑¯10↑↓attrib ⎕nl 3 4  ⍝ What's new?            
      ⍕notes find 'Word'    ⍝ Apropos "Word".        
      ⎕ed'notes.contents'   ⍝ Workspace overview.    
                                                     
      ⎕io←0
      roots     ← {×\1,1↓(⍵÷2)⍴¯1*2÷⍵} 
      cube      ← {⍵⍴⍨2⍴⍨2⍟⍴⍵} 
      extend    ← {(2*⌈2⍟¯1+(⍴⍺)+⍴⍵)↑¨⍺ ⍵} 
      floop     ← {(⊣/⍺)∇⍣(×m)⊢(+⌿⍵),[m-0.5]⍺×[⍳m←≢⍴⍺]-⌿⍵} 
      FFT       ← {      ,(cube  roots ⍴⍵)floop cube ⍵} 
      iFFT      ← {(⍴⍵)÷⍨,(cube +roots ⍴⍵)floop cube ⍵} 
      ⍝ ... etc

[Stu]

I tried again, this time in a clean workspace. It works fine. I don't know why that last expression wouldn't work in my original workspace. Sorry for the trouble!