Why I have wrong result in (power) function?

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Abdulatif Alabdulatif 2014-11-7

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评论： Star Strider 2014-11-8

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Hi all,

I have the following statement which generate wrong result:

temp1 = power(x,temp1)

The wrong result is:

temp1 =
     Inf

if I change ( temp1 ) to a number it works! but f I use a variable (temp), it does not work.

Any help?

Thank you

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Star Strider 2014-11-7

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The variables x and temp1 have to be numeric in core MATLAB, as it seems you are doing.

If you’re doing symbolic calculations, you need to use the Symbolic Math Toolbox.

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Abdulatif Alabdulatif 2014-11-8

编辑：Abdulatif Alabdulatif 2014-11-8

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I have to perform modulus operation after find the power result.

x=3
temp1= 25111
temp1 = power(x,temp1)
result = mod(temp1,7);

Is it possible to perform (mod) operation with float-point numbers?

I already found alternative solution by perform (for loop) but it is slow in term of performance.

Star Strider 2014-11-8

I doubt that what you want to do is possible. At least I can’t imagine how to do it, because it would involve both division and subtraction, and that would involve raising some multiple of 7 far beyond the ability of MATLAB floating-point precision in order to do the subtraction. (I doubt if it would even be possible to factor it.)

I don’t know how you could do this with a for loop, because you could not represent 3^25111 in MATLAB at all, to the best of my knowledge. I can envision doing it in assembler with serial multiplications of 3 then serial divisions by 7, but that isn’t something I’d want to do.

If you did manage to solve this with for loops, please post your code.

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