       Re: How to remove all cycles

• To: mathgroup at smc.vnet.net
• Subject: [mg98316] Re: [mg98269] How to remove all cycles
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 5 Apr 2009 06:41:08 -0400 (EDT)

```n = 13;

A = Array[a, 2^(n + 1)];

B = Array[b, {2, 2^n}];

Do[Do[A[[j + BitShiftLeft[k - 1, 1]]] = B[[j, k]], {j, 1, 2}], {k, 1,
2^n}] // Timing

{0.616373,Null}

A2 = Flatten[Transpose[B]]; // Timing

{0.008281,Null}

A == A2

True

Bob Hanlon

---- buts <manger31 at yahoo.com> wrote:

=============
Hello,
I want to write the following code using functional
programming, i.e. to remove all Do's.
There are two arrays:

A[[i]], i=1,...,2^(n+1)
B[[j,k]], j=1,2;  k=1,...,2^n.

I need to assign B to A setting the first bit of the index i
to be the index j. Explicitly

Do[Do[A[[ j + BitShiftLeft[k-1,1] ]]= B[[j,k]],
{j,1,2}],{k,1,2^n}]

I need to do it for multi-dimensional large arrays.
Is it possible to write it without Do's ?

Thanks.

--

Bob Hanlon

```

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