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Multiplication using bc in a for loop

 
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# 1  
Old 11-30-2009
Multiplication using bc in a for loop
Hi,
I would like to carry out a multiplication in a for loop but some how I get always zero. The result of the multiplication must be assigned to the variable x.
Here is teh code

Code:
for (( i=1;i<=15;i++)); do
    x=$( printf "%s\n " 'scale = 10; i*5.0*335.0*3.0/1000.0' | bc)
    echo $x $i
done

Thanks,
Sarah
# 2  
Old 11-30-2009
Hi.

"i" is a variable, so...

Code:
for (( i=1;i<=15;i++)); do
    x=$( printf "%s\n " "scale = 10; $i*5.0*335.0*3.0/1000.0" | bc)
    echo $x $i
done

(and notice the double quotes around the "scale =" string)
# 3  
Old 11-30-2009
Quote:
Originally Posted by scottn
Hi.

"i" is a variable, so...

Code:
for (( i=1;i<=15;i++)); do
    x=$( printf "%s\n " "scale = 10; $i*5.0*335.0*3.0/1000.0" | bc)
    echo $x $i
done

(and notice the double quotes around the "scale =" string)
yes I had tried with $i but I got an error message

Code:
(standard_in) 1: illegal character: $

With the double qutes is fine, thank you!

---------- Post updated at 08:56 AM ---------- Previous update was at 06:04 AM ----------

Hi again,
I have some problems with 'bc'

Code:
for (( i=1;i<=15;i++)); do
     x=$( printf "%s\n " "scale = 10; $i*5.0*335.0*3.0/1000.0" | bc)
     y=$(/cygdrive/u/TOOLS/extract_v04d 1 yyy1 $i $i S 1 x x)
    dy=$( printf "%s\n " "scale = 10; $y * 0.05" | bc)
    echo $x $x $y $dy $z $dz >> fit.dat
done

in y I have a value that I read with another program from a file. The value of y is correct, but when I try to calculate the 5% of y I get a non sense.
e.g. the output is
Code:
 5.0250000000  5.0250000000 6.324E+08 6.7249 
10.0500000000 10.0500000000 1.304E+09 1.7549 
15.0750000000 15.0750000000 2.185E+09 2.6359 
20.1000000000 20.1000000000 3.248E+09 3.6989

I suppose the meaning of scale in bc is the scale to use to carry out the calculation(10 for decimal)

Does anybody know what am I doing wrong?
Thanks
# 4  
Old 11-30-2009
Quote:
...
I suppose the meaning of scale in bc is the scale to use to carry out the calculation(10 for decimal)
...
No, scale=10 means that the output is formatted with 10 digits after the decimal point.

Excerpt from the manpage of bc:
scale ( expression ) The value of the scale function is the number of digits after the decimal point in the expression.
# 5  
Old 11-30-2009
Quote:
Originally Posted by toto
No, scale=10 means that the output is formatted with 10 digits after the decimal point.

Excerpt from the manpage of bc:
scale ( expression ) The value of the scale function is the number of digits after the decimal point in the expression.
I guess my problem is that bc doesn't like having numbers in scientific format...
any help is welcome on how to solve the problem
# 6  
Old 11-30-2009
According to your output the value of y is coming back as a scientific number.

Try either changing the program that returns it to return a decimal number, or convert it using something like:

Code:
y=$(/cygdrive/u/TOOLS/extract_v04d 1 yyy1 $i $i S 1 x x | awk '{printf("%d", $1)}')

 
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