1) That's not a multi-dimensional array, that's a one-dimensional array simulating a multi-dimensional array.

2) Why not

    arr[n1 + i][n2 + j][n3 + j] = calc_foo(i,j,k)

? It's a bit more work to write the proxy classes, but a Sufficiently Smart Compiler(TM) can make that all go away for you.