how to use bc to handle numbers in scientific/exponential notation?

zero79 · 08-10-2004, 01:05 PM

i'm trying to manipulate numbers that are in exponential notation (for example 3.8678E-5) using the gnu bc calculation tool. it doesn't seem to support the above notation.

what i want to do is comare two numbers to determine which is larger. this is my idea of what the script would look like if bc supported exponential notation

Code:

!/bin/bash
a=5.083E-5
b=7.0134
echo "if ($a > $b); then echo $a; else echo $b; fi" | bc

$a and $b are arbitrary values written in scientific notation. i've tried parsing the values into a decimal and a power using 'awk,' but this won't work if i end up with a number that does not need to be represented in scientific notation (such as $b in the above script). i really appreciate any thoughts on this. thanks.

Tinkster · 08-10-2004, 02:35 PM

awk -F"E" '{print $1 * ( 10 ^ $2)}'

would work, but the problem is that awk also
uses scientific notation once the number exceeds
a given level ...
Taking the number from your example this is
what happens:
[tink@diggn:~]$ echo "5.083E-5" | awk -F"E" '{print $1 * ( 10 ^ $2)}'
5.083e-05

[edit]
Btw, I'm not quite sure what you're trying to achieve
by echoing a single number into bc?

Having toyed around a bit more I came up with
this one ...

Code:

echo "5.083E-5" | awk -F"E" 'BEGIN{OFMT="%10.10f"} {print $1 * (10 ^ $2)}'  
0.0000508300

[/edit]

Cheers,
Tink

rahul.garg · 08-06-2008, 04:25 PM

Hi Guys,
I'm stuck with a similar problem.
I'm trying to add two numbers using bc. Both the numbers are in exponent form. THe command is

FDRAGAVG[${index}]=`echo "scale=16 ; (${FDRAGAVG[${index}]}+${fdrag})" | bc`

Since the bc does not recognize the exponent precision, all that information is being lost.

Can someone please suggest me a better way to add up numbers in exponent notation in bash script

Thanks for the help.
Rahul

zero79 · 09-14-2008, 10:36 PM

can you post the rest of your script? something to test out, and fiddle to get working?