Why I have wrong result in (power) function?

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Abdulatif Alabdulatif
Abdulatif Alabdulatif on 7 Nov 2014
Commented: Star Strider on 8 Nov 2014
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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Answers (1)

Star Strider
Star Strider on 7 Nov 2014
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
Abdulatif Alabdulatif on 8 Nov 2014
Edited: Abdulatif Alabdulatif on 8 Nov 2014
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
Star Strider on 8 Nov 2014
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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