Question

I have a very large table in Mathematica ((dimcub-1)^3 elements) coming from an inverse FFT. I need to use periodic interpolation on this table. Since periodic interpolation requires that the first elements and last elements are equal, I create a new table of dim^3 elements manually and use that in my interpolation. It works but it is ugly/slow and due to my superfluous intermediate table, I hit the memory barrier sooner. Can any one tell me either how to turn my old table into a periodic one somehow by appending elements or use my non periodic table to make a periodic interpolation function? Here is my current piece of code:

mr 1 is the new table:

mr1 = Table[  0. , {i, 1, dimcub}, {j, 1, dimcub}, {k, 1, dimcub}];

Do[Do[  Do[   
      mr1[[m, n, k]] = oldtable[[m, n, k]] ;  , {m, 1, 
       dimcub - 1}]; , {n, 1, dimcub - 1}]; , {k, 1, dimcub - 1}]; 
Do[Do[     mr1[[m, n, dimcub]] =  mr1[[m, n, 1]]; 
  mr1[[m, dimcub, n]] =  mr1[[m, 1, n]];  
  mr1[[dimcub, m, n]] =  mr1[[1, m, n]];     , {m, 1, dimcub - 1}];  
 mr1[[n, dimcub, dimcub]] =  mr1[[n, 1, 1]]; 
 mr1[[dimcub, n, dimcub]] =  mr1[[1, n, 1]];  
 mr1[[dimcub, dimcub, n]] =  mr1[[1, 1, n]]; , {n, 1, dimcub - 1}]; 
mr1[[dimcub, dimcub, dimcub]] = mr1[[1, 1, 1]]; 

Remove[oldtable]; 

myinterpolatingfunction = 
 ListInterpolation[mr1, {{1, dimcub}, {1, dimcub}, {1, dimcub}}, 
  InterpolationOrder -> 1, 
  PeriodicInterpolation -> True];

 Remove[mr1];

myinterpolatingfunction takes much less memory and works perfectly once i remove the older tables. Any help will be greatly appreciated.

Answer 1

Thanks for all the answers. I tried the suggestion by leonid but when I print my oldtable, it was still (dimcub -1)^3 dimensional. New elements were defined and I can see them individually but they do not show up as part of the oldtable when I print the whole table. So I ended up with something similar which is doing exactly what I needed:

oldtable= PadRight[oldtable, {dimcub, dimcub, dimcub}];
oldtable[[All, All, dimcub]] = oldtable[[All, All, 1]];
oldtable[[All, dimcub, All]] = oldtable[[All, 1, All]];
oldtable[[dimcub, All, All]] = oldtable[[1, All, All]];
oldtable[[All, dimcub, dimcub]] = oldtable[[All, 1, 1]];
oldtable[[dimcub, All, dimcub]] = oldtable[[1, All, 1]];
oldtable[[dimcub, dimcub, All]] = oldtable[[1, 1, All]];
oldtable[[dimcub, dimcub, dimcub]] = oldtable[[1, 1, 1]];

The answer by Wizard is far too advanced for my level of mathematica..