gnuplot-info

[Gnuplot-info] The use of $ in scripts and simple data transformations in scripts

[Beyer <bey...@gm...>]

I have a data file where column one is the x-values. The second column is a
measure of current and the third is a measure of the potential drop across a
device.
I need to plot the conductance of the device which means I have to take
column 2 and divide it with column 3.
Something like plot 'bla.dat' u 1:($2/$3)
U = IR >> U/I = R >> I/U = 1/R = G

Now I am making a multiplot since I am comparing five different graphs and I
am doing this by calling a script that works fine just plotting the current
alone, for example. The problem comes when I try to follow the example given
in "gnuplot in action" on page 41.
that says: "If an argument to using is enclosed in parentheses, it’s not
treated as a column number, but as an expression to be evaluated. Inside the
parentheses,
you can access the values of the column values for the current record by
preceding
the column number with a dollar sign ($) (as in shell or awk programming).
Some examples will help to clarify.

...

To plot the average of the second and third columns, use
plot "data" using 1:( ($2+$3)/2 ) with lines"

MY PROBLEM IS:

CODESNIPPET FROM MY SCRIPT:
plot '$3.dat' u 1:($2/$3) w l ls 1

now the example in the book seems to indicate I have to use the dollar sign
in the parenthesis to indicate that I am talking about a column number in
the expression but when gnuplot reads the script it quite naturally seems to
read the two values as the fourth and third option fed to the script when I
call it from gnuplot.
This clearly isn't what I really want it to do, but I can't figure out how I
tell gnuplot that the $3 means "column three" not "script option 4"
-----------------
I call the script by calling:
call 'multi.gp' 'firstmultitest' '3' '2' 'datafile' 'datafile2' 'datafile3'
'datafile4' 'datafile5'

The script as it appears now looks like:
#0=filename for the final graph 1=number of rows 2=number of columns 3=data
filename 4=data filename 5=data filename 6=data filename 7=data filename
8=data filename
set terminal push
set output "$0.png"
set style line 1 lt -1 lw 2
set terminal png size 1000,600 font Arial 16
set multiplot layout $1,$2
unset key
unset tics
set ytics 0,0.1 nomirror
set xtics -10,2.5 nomirror
unset border
set border 3 lt -1 lw 2
plot '$3.dat' u 1:($2/$3) w l ls 1
plot '$4.dat' u 1:(2/3) w l ls 1
plot '$5.dat' u 1:(2/3) w l ls 1
plot '$6.dat' u 1:(2/3) w l ls 1
plot '$7.dat' u 1:(2/3) w l ls 1
#plot '$8.dat' u 1:(3) w l ls 1 #not needed yet
unset multiplot
replot
set output
set terminal pop


Thank you very much for your help.

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Re: [Gnuplot-info] The use of $ in scripts and simple data transformations in scripts

[Thomas S. <t.s...@fz...>]

gnuplot manual or 'help call' says:

NOTE: there is a clash in syntax with the datafile using callback
operator. Use $$n or column(n) to access column n from a datafile
inside a called datafile plot.


Beyer wrote:
> 
> I have a data file where column one is the x-values. The second column is
> a measure of current and the third is a measure of the potential drop
> across a device.
> I need to plot the conductance of the device which means I have to take
> column 2 and divide it with column 3.
> Something like plot 'bla.dat' u 1:($2/$3)
> U = IR >> U/I = R >> I/U = 1/R = G
> 
> Now I am making a multiplot since I am comparing five different graphs and
> I am doing this by calling a script that works fine just plotting the
> current alone, for example. The problem comes when I try to follow the
> example given in "gnuplot in action" on page 41.
> that says: "If an argument to using is enclosed in parentheses, it’s not
> treated as a column number, but as an expression to be evaluated. Inside
> the parentheses,
> you can access the values of the column values for the current record by
> preceding
> the column number with a dollar sign ($) (as in shell or awk programming).
> Some examples will help to clarify.
> 
> ...
> 
> To plot the average of the second and third columns, use
> plot "data" using 1:( ($2+$3)/2 ) with lines"
> 
> MY PROBLEM IS:
> 
> CODESNIPPET FROM MY SCRIPT:
> plot '$3.dat' u 1:($2/$3) w l ls 1
> 
> now the example in the book seems to indicate I have to use the dollar
> sign in the parenthesis to indicate that I am talking about a column
> number in the expression but when gnuplot reads the script it quite
> naturally seems to read the two values as the fourth and third option fed
> to the script when I call it from gnuplot.
> This clearly isn't what I really want it to do, but I can't figure out how
> I tell gnuplot that the $3 means "column three" not "script option 4"
> -----------------
> I call the script by calling:
> call 'multi.gp' 'firstmultitest' '3' '2' 'datafile' 'datafile2'
> 'datafile3' 'datafile4' 'datafile5'
> 
> The script as it appears now looks like:
> #0=filename for the final graph 1=number of rows 2=number of columns
> 3=data filename 4=data filename 5=data filename 6=data filename 7=data
> filename 8=data filename
> set terminal push
> set output "$0.png"
> set style line 1 lt -1 lw 2
> set terminal png size 1000,600 font Arial 16
> set multiplot layout $1,$2
> unset key
> unset tics
> set ytics 0,0.1 nomirror
> set xtics -10,2.5 nomirror
> unset border
> set border 3 lt -1 lw 2
> plot '$3.dat' u 1:($2/$3) w l ls 1
> plot '$4.dat' u 1:(2/3) w l ls 1
> plot '$5.dat' u 1:(2/3) w l ls 1
> plot '$6.dat' u 1:(2/3) w l ls 1
> plot '$7.dat' u 1:(2/3) w l ls 1
> #plot '$8.dat' u 1:(3) w l ls 1 #not needed yet
> unset multiplot
> replot
> set output
> set terminal pop
> 
> 
> Thank you very much for your help.
> 
> 

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