Matrix X.^23 without approximation

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Sakunrat Jaejaima
评论： bio lim 2015-7-10
I want to get the answer with no approximation,
I have X=[25 24 23;27 8 11]
I want X.^23 without approximation,help me please.

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回答（3 个）

Torsten
Torsten 2015-7-8
Apply Titus' answer under
http://www.mathworks.com/matlabcentral/answers/227104-25-23-without-approximation
to each element of X.
Best wishes
Torsten.
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Titus Edelhofer
Titus Edelhofer 2015-7-8
X.^23
is the same as
[x(1,1)^23 x(1,2)^23
x(2,1)^23 ...]
so apply the technique in my answer to the last time you asked this question to each single entry in your matrix.

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bio lim
bio lim 2015-7-8
What do you mean by without approximation? Are you talking about scientific notations? If so, you can change the format using, format style.
X=[25 24 23;27 8 11];
format bank % I am guessing this is the format you want.
X.^23
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Steven Lord
Steven Lord 2015-7-8
You will need to compute in higher precision than double. 25^23 is large enough that not all integers that are that large can be exactly represented.
25^23 > flintmax
In fact, 25^23 is so large that even 1,000,000 is negligible compared to it.
z1 = 25^23;
z2 = z1 + 1000000;
z1 == z2 % will return TRUE, this is NOT a bug!
Think of it as though you gave Bill Gates a $5 bill. He's so rich ($78.8 billion according to Wikipedia) that $5 doesn't change his net worth at all. [Contacting the necessary accountants to change his net worth would cost him more than the $5 you gave him!]
You can compute symbolically:
X = sym([25 24 23;27 8 11]);
X.^23
Or if you're doing this as part of computing 25^23 mod N for some value N, don't compute 25^23 first then compute MOD. That's the straightforward approach described on the "Modular exponentiation" Wikipedia page, but it breaks down when the quantity whose modulus you're taking gets too large. Instead apply one of the other techniques described on that page. For small exponents, the memory efficient method is easy to write; the right-to-left is a little more difficult, but using BITGET you can do it reasonably easily in MATLAB.

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