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How do I round off exponential numbers?

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Nitin Samuel
Nitin Samuel 2013-1-17
评论： Walter Roberson 2015-11-16
I have a code for which I get a long exponential number eg. a = 2.572920056e-3 as the output. I need to round off only the non-exponential part i.e I want the output to be something like 2.573e-3.
I know how to round off integers using ceil, round etc, but how can one round off only the number outside the exponential like mentioned above. Also, the output varies so I cannot use a command with a fixed number like
(ceil(a*10^6)/10^6).
(The fixed number being '6' in this case).

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Walter Roberson
Walter Roberson 2013-1-17
编辑：Walter Roberson 2013-1-17
ex = 10^(3-floor(log10(a)));
ar = round(a * ex) / ex;
Caution: might not work for 0 or infinities
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Mikhail Lisakov
Mikhail Lisakov 2015-11-16
编辑：Walter Roberson 2015-11-16
Solution is great but fails for powers > 0 (though I've used it to round significand to integer).
To account for possible powers greater than 0 there should be a condition like this :
if(ex < 0)
ar = round(a * ex) / ex;
} else {
ar = round(a / ex) * ex;
}
Walter Roberson
Walter Roberson 2015-11-16
Different requirement, Mikhail. That formula would be for rounding decimals after the decimal point in fixed point format, but the original question was for rounding in engineering format.

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