gnuplot 'set title' with sprintf : representing angle in terms of fractions of pi

Question

I'd like to run a gnuplot .inp file so all the angles in the script show up automatically in the title as fractions based on the Greek letter pi - instead of a decimal form for the angle. I already know how to use {/Symbol p}, but that is a manual intervention that is impractical in this case.

I have an example sprintf line in a gnuplot input file which can produce nice title information :

   angle=( (3*pi) /4 )
   set title sprintf ("the angle is %g radians", angle)
   plot sin(x)

... the output file (e.g. svg) or terminal (e.g. wxt) shows "2.35619", which is correct, however ; it would be nice to see the Greek letter for pi and the fraction itself, as is typically read off of a polar plot, e.g " 3/4 pi". Likewise for more complex or interesting representations of pi, such as "square root of two over two".

I already know I can manually go into the file and type in by hand "3{/Symbol p}/4", but this needs to be done automatically, because the actual title I am working with has numerous instances of pi showing up as a result of a setting of an angle.

I tried searching for examples of gnuplot being used with sprintf to produce the format of the angle I am interested in, and could not find anything. I am not aware of sprintf being capable of this. So if this is in fact impossible with gnuplot and sprintf, it will be helpful to know. Any tips on what to try next appreciated.

UPDATE: not a solution, but very interesting, might help :

use sprintf after the 'plot' to set the title that appears in the key (but not the overall title):

gnuplot setting line titles by variables

so for example here, the idea would be :

foo=20
plot sin(x)+foo t sprintf ("The angle is set to %g", foo)```

Answer 1

I have [1] a workaround below that might be feasible, and [2] apparently what I was looking for below that (I am writing this in haste). I will mark the question "answered" anyway. To avoid reproducing theozh's script, I offer :

[1]:

1. add three lines to theozh's script - ideally, immediately before the 'plot' command :

   set title sprintf ("Test: %g $\\sqrt{\\pi \\pi \\pi \\pi}$", pi)
   set terminal tikz standalone
   set output 'gnuplot_test.tex'

one can observe a little testing going on with nonsensical expressions of pi - it is just to see the vinculum extend, and this is a hasty thing - and the double-escapes - they appear to have made it to Stack Overflow correctly.

2. change the 'plot' line to remove the Times Roman part, but this might not be necessary :

plot $Data u (0):0:(fPi($1)) w labels

3. importantly, edit gnuplot_test.tex so an \end{document} is on the last line.

4. run 'pdflatex gnuplot_test.tex'.

This should help move things along - it appears the best approach is to go into the LaTeX world for this - thanks. I tried cairolatex pdf and eps but I was very confused with the LaTeX output. the tikz works almost perfectly.

[2]: What I was looking for : put this below the fPi(x) expression in gnuplot :

set title sprintf ("Testing : \n wxt terminal : \
%g %s %s %s \n tikz output : $\\sqrt{\\pi \\pi \\pi \\pi}$", \
pi, fPi(myAngle01), fPi(myAngle02), fPi(myAngle03) )
# set terminal tikz standalone
# set output 'gnuplot_test.tex'
plot $Data u (0):0:(fPi($1)) w labels t sprintf ("{/Symbol p}= %g, %s, %s, %s, %s", \
pi, fPi(pi), fPi(myAngle01), fPi(myAngle02), fPi(myAngle03) )

... the wxt terminal displays the angles as fractions of pi. I didn't test the output in the LaTeX pipeline - remove if undesired. I think the gnuplot script has to be written for the terminal or output desired - but at least the values can be computed - instead of writing them in "manually".

Answer 2

Here is an attempt to define a function to find fractions of Pi. Basically, sum (check help sum) is used to find suitable multiples/fractions of Pi within a certain tolerance (here: 0.0001). It is "tested" until a denominator of 32. If no integer number is found, the number itself is returned. In principle, the function could be extended to find multiples or fractions of roots, sqrt(2) or sqrt(3), etc. This approach can certainly be improved, maybe there are smarter solutions.

Script:

### format number as multiple of pi
reset session

$Data <<EOD
 1.5707963267949
-1.5707963267949
 6.28318530717959
 2.35619449019234
 2.0943951023932
-0.98174770424681
 2.24399475256414
 1.0
 1.04
 1.047
 1.0471
 1.04719
EOD

set xrange[-10:10]
set yrange[:] reverse
set offset 0.25,0.25,0.25,0.25
set key noautotitle

dx = 0.0001
fPi(x) = (_x=x/pi, _p=sprintf("%g",x), _d=NaN, sum [_i=1:32] \
         (_d!=_d && (abs(_x*_i - floor(_x*_i+dx)) < dx) ? \
         (_n=floor(_x*_i+dx),_d=_i, \
         _p=sprintf("%sπ%s",abs(_n)==1?_n<0?'-':'':sprintf("%d",_n),\
          abs(_d)==1 ? '' : sprintf("/%d",_d)),0) : 0 ), _p)

plot $Data u (0):0:(fPi($1)) w labels font "Times New Roman, 16"
### end of script

Result: