functions in fft.i - r

    roll(x, ljoff, rjoff)  
 or roll, x, ljoff, rjoff  
 or roll(x)  
 or roll, x  


"rolls" selected dimensions of the array X.  The roll offsets  
LJOFF and RJOFF (both optional) work in the same fashion as the  
LJDIR and RJDIR arguments to the fft function:  
   A scalar LJDIR (and nil RJDIR) rolls all dimensions of X by  
   the specified offset.  
   Otherwise, the elements of the LJDIR vector [ljoff1, ljoff2, ...]  
   are used as the roll offsets for the first, second, etc.  
   dimensions of X.  
   Similarly, the elements of the RJDIR vector [..., rjoff1, rjoff0]  
   are matched to the final dimensions of X, so the next to last  
   dimension is rolled by rjoff1 and the last dimension by rjoff0.  
   As a special case (mostly for use with the fft function), if  
   both LJDIR and RJDIR are nil, every dimension is rolled by  
   half of its length.  Thus,  
      roll(x)  
   it equivalent to  
      roll(x, dimsof(x)(2:0)/2)  
The result of the roll function is complex if X is complex, otherwise  
double (i.e.- any other array type is promoted to type double).  If  
roll is invoked as a subroutine, the operation is performed in place.  
Interpreted function, defined at i0/fft.i   line 254