On Dec 8, 2004, at 7:43 AM, Raymond Toy wrote:
>>>>>> "rif" == rif <[EMAIL PROTECTED]> writes: > > rif> Is there any way, in CMUCL, using some implementation-specific > rif> construct, to create an "aliased array"? Suppose I create a > rif> double-float array of size 10: > > rif> (make-array 10 :element-type 'double-float) > > rif> I know I can take it's address, with #'system:vector-sap. > > rif> What I want to do is manipulate that address and somehow > "invert" > rif> vector-sap to create a new double-float array whose first > element is > rif> (for example) the third element of the original array. > > rif> I need this because I need to pass matlisp a subset of an > array. More > rif> specifically, I want to allocate an n by n+1 array, so that I > can > rif> store half of each of two n by n symmetric arrays in n(n+1) > space > rif> rather than 2n^2 space. This is a common technique for using > rif> BLAS/LAPACK, but to get at it, I need to be able to give a > Fortran > rif> matlisp routine a way to get at the square n by n matrix that > "starts > rif> with the second column" of the n by n+1 matrix, and the way > the > rif> interface is defined, it wants actual arrays, not pointers. > If I can > rif> somehow create the appropriate array, I don't have to go > mucking about > rif> in the internals of matlisp's def-fortran-routine and so > forth. > > Marc has already mentioned displaced arrays. This should work, but > depends on what you are really trying to do. Not necessarily. Displaced arrays are good for row-major slices. So if the matrix where (N + 1 x N), then you could "displace away" the first row. Unfortunately, FORTRAN is column-major. The only way I see around this is to transpose the array first, and then displace. However, that may cause problems for the algorithm at hand. Isn't this fun? :) Cheers -- Marco Antoniotti http://bioinformatics.nyu.edu NYU Courant Bioinformatics Group tel. +1 - 212 - 998 3488 715 Broadway 10th FL fax. +1 - 212 - 998 3484 New York, NY, 10003, U.S.A.
