matrix and fibonacci

[newcomer[bob]]

On Friday, 9 March 2012 at 09:22:47 UTC, newcomer[bob] wrote:
> On Friday, 9 March 2012 at 05:50:03 UTC, newcomer[bob] wrote:
>> The following is a matrix implementation of the fibonacci
>> algorithm:
>>
>> int fib(int n)
>> {
>>     int M[2][2] = {{1,0},{0,1}}
>>     for (int i = 1; i < n; i++)
>>         M = M * {{1,1},{1,0}}
>>     return M[0][0];
>>  }
>>
>> problem is I don't really understand how matrix multiplication
>> works so i cannot translate it to an equivalent solution in D.
>> Thank for you assistance in advance.
>>
>> newcomer[bob]
>
> I attempted the following but it does not work:
>
> int fib(int n)
>      long[2][2] M = [[1,0], [0,1]];
>      ulong[2][2] C = [[1,1], [1,0]];
>      foreach (i; 0 .. n) {
>      	M[0][0] = M[0][0] * C[0][0] + M[0][0] * C[0][1];
>      	M[0][1] = M[0][1] * C[0][1] + M[0][1] * C[1][1];
>      	M[1][0] = M[0][1] * C[0][0] + M[1][1] * C[0][1];
>      	M[1][1] = M[1][1] * C[0][1] + M[1][1] * C[1][1];
>      }
>      return M[0][0];
> }
>
> any ideas what I'm doing wrong?
>
> Thanks,
> Bob

Turns out that this this is an algorithm for calculating the
powers of two up to 2^63. I still cannot find how to modify it to
produce the fibonacci sequence though. Any advice would be
appreciated.

Thanks,
Bob