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I want to raise a fraction (fraction is calculated on first loop) to a decimal power (second loop), however, I always get 1 as a result. I want to store the output of the second loop in an array as well. Any ideas how to work around this? Thank you!

#
# vector of vertical pressure levels
levs=($(seq 200.0 50.0 900.0))
printf "%s\n" "${levs[@]}"
#
# exponent for dry air
rho=$(bc -l <<<'e(l(0.0819)*0.5)')
echo $rho
#
# calculate fraction of P_surf/P_i from Poisson equation for each vertical pressure level
val3=()
#
for i in "${levs[@]}"
 do
   echo $i
   val3+=($(bc -l <<<"1000.0/$i"))
   echo "$val3"
 done
printf "%s\n" "${val3[@]}"
#
# raise fraction of P_surf/P_i to the rho power for dry air (#bc <<< "2 ^ 3")
pow=()
#
for j in "${val3[@]}"
 do
   echo $j
   echo $rho
   pow+=($(bc <<<"$j^rho"))
   #echo $((i*rho))
   echo "$pow"
 done
#
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There are a couple of problems associated with your attempt. The immediate problem being using rho as a literal string when raising it as a power constant to bc

bc <<<"$j ^ $rho"

Even with that the code does not work, bc does not take fractional numbers for exponents. You get an error non-zero scale in exponent.

You can use awk (tested on GNU variant) for the same and apply the equal precision formatting as

awk -v base="$j" -v xp="$rho" 'BEGIN{ printf "%.20f", base ** xp }'
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  • 1
    The OP already uses e(l(0.0819)*0.5) in place of 0.0819 ^ 0.5 (where they could have used sqrt(0.0819)), so here, that could just as well use e(l($j)*$rho) Commented Oct 9, 2019 at 10:50

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