Issues with set_axis

[14NGiestas]

First of all, good job.
I noticed some issues with the function set_axis:

1. There is a problem with small numbers and the descriptor F0.0 you are using there.
   I passed this vector to the function:

[-2.0943951023931956E-002,  0.13463968515384828 ,      -5.0000000000000000,        200.00000000000000]

And this is the output:

set xrange [-0.:0.]
set yrange [-5., 200.]

which gives me a error

"ogpf_temp_script.gp" line 6953: Can't plot with an empty x range!

2. The interface don't allow to set one specific range like yrange or zrange without having to set the xrange
   I suggest using optional arguments to set each individual argument or maybe writing 3 new methods to each one

subroutine set_axis(this, xrange, yrange, zrange)
       class(gpf):: this
       real(wp), optional, intent(in) :: xrange(2)
       real(wp), optional, intent(in) :: yrange(2)
       real(wp), optioanl, intent(in) :: zrange(2)
       if (present(xrange)) then
               this%hasxrange=.true.
               this%xrange=xrange
       end if
       if (present(yrange)) then
               this%hasyrange=.true.
               this%yrange=yrange
       end if
       if (present(zrange)) then
               this%haszrange=.true.
               this%zrange=zrange
       end if
end subroutine

[kookma]

@14NGiestas

I do not understand your first question: set xrange [-0.:0.] means plot on empty range and it returns by gnuplot NOT ogpf library.

For the second question: The method is a clone of axis in Matlab, but what you proposed is more flexible in comparison to the current procedure. I will apply this in the next release!

By the way: Feel free to modify the code, test and see if it works! Then you can inform me to update the code! If you know how to submit a PR do it please.

[14NGiestas]

I mean when I set the axis using your function set_axis the output file generated by the library is wrong (the actual output is made by ogpf despite the error being thrown by gnuplot). In the subroutine processcmd there is a descriptor Fw.d to write the range stuff, however the decimal places "d" is set to zero rounding small numbers to zero at the output.
I fixed the issue by setting a non-zero decimal place, for eg.: replacing "F0.0" with "F0.3". But I'm sure this is not the best descriptor either, maybe a scientific notation or the G descriptor would be better:
intel reference to G descriptor
stack overflow mention to G0 descriptor

[14NGiestas]

PR done #6

[14NGiestas]

Closing the issue since the related PR was merged. I'm going to open another specific one related to the interface.

[kookma]

@14NGiestas Thank you!

Please consider backward compatibility! The headers almost very similar to Octave and Matlab!

[14NGiestas]

@14NGiestas Thank you!

Please consider backward compatibility! The headers almost very similar to Octave and Matlab!

Sure! I've introduced some samples to discuss in the issue #9