Condense
From NARS2000


R is an arbitrary Real numeric array (BOOL, INT, FLT, APA, RAT, VFP — otherwise, DOMAIN ERROR) whose number of columns (≢R) is 1, 2, 4, or 8 — otherwise, LENGTH ERROR.  
Z is the corresponding Real or Hypercomplex array of shape ¯1↓⍴R using the columns of R as the coefficients of the resulting Real or Hypercomplex array. If ≢R is 1, the result is the Real array (¯1↓⍴R)⍴R, if ≢R is 2, the result is a Complex array, if ≢R is 4, the result is a Quaternion array, and if ≢R is 8, the result is an Octonion array. 
For example,
<23
23
<10 20
10J20
<2 4⍴⍳8
1i2j3k4 5i6j7k8
<2 8⍴(⍳8),⌽⍳8
1i2j3k4l5ij6jk7kl8 8i7j6k5l4ij3jk2kl1
⍴⎕←<2 3 1⍴⍳6
1 2 3
4 5 6
2 3
⍴⎕←<2 3 2⍴(⍳6),⌽⍳6
1J2 3J4 5J6
6J5 4J3 2J1
2 3
⍴⎕←<2 3 4⍴(⍳12),⌽⍳12
1i2j3k4 5i6j7k8 9i10j11k12
12i11j10k9 8i7j6k5 4i3j2k1
2 3
⍴⎕←<2 3 8⍴(⍳24),⌽⍳24
1i2j3k4l5ij6jk7kl8 9i10j11k12l13ij14jk15kl16 17i18j19k20l21ij22jk23kl24
24i23j22k21l20ij19jk18kl17 16i15j14k13l12ij11jk10kl9 8i7j6k5l4ij3jk2kl1
2 3
Identities
R ←→ <>R for all R (see Dilate for the definition of monadic Right Caret)
R ←→ ><R for all R with (¯1↑⍴R)∊1 2 4 8
Acknowledgements
This symbol and its name were suggested by David A. Rabenhorst.