CODEWITHSUNDEEP
loopsgnuplot
chocolate.broccoli
chocolate.broccoli

Reputation: 139

gnuplot--iteration to obtain variables in datafile

Let's say that I've got data called 'myData.dat' in the form

x  y
0  0
1  1
2  2
4  3
8  4
16 5

I need to find the following things from this data:

Then I need to plot the the data and overlay the lines; below is a picture of what I'm asking for.

enter image description here

I know how to obtain the the slope and y-intercept for a single pair of points, and plot the data and the equation of the line. For example for points 1 and 5:

set table
plot "myData.dat" using 0:($0==0 ? y1=$2 : $2)
plot "myData.dat" using 0:($0==4 ? y5=$2 : $2)
unset table

m1 = (y5 - y1)/(5-1)
b1 = y1 - m1*1
y1(x) = m1*x + b1

I'm new to iteration (and gnuplot) and I think there's something wrong with my syntax. I've tried a number of things and they haven't worked. My best guess is that it would be in the form

plot for [i=1:4] using 0:($0==1 ? y.i=$1 : $1)

do for [i=1:5]{
m.i = (y5 - y.i)/(5-i)
b.i = y.i - m.i*1
y.i(x) = m.i*x + b.i    
}

set multiplot
plot "myData.dat" w lp
plot for [i=1:4] y.1(x)
unset multiplot

So what is going wrong? Is gnuplot able to concatencate the loop counter to variables?

Upvotes: 1

Views: 741

Answers (1)

Miguel
Miguel

Reputation: 7627

Your syntax is incorrect. Although there are other ways to do what you want, for instace using word(var,i), the most straightforward fix to what you already have would be to use eval to evaluate a string to which you can concatenate variables:

do for [i=1:5]{
eval "m".i." = (y5 - y".i.")/(5-".i.")"
eval "b".i." = y".i." - m".i."*1"
eval "y".i."(x) = m".i."*x + b".i    
}

Upvotes: 1

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