xmaxima plotdf doesn't allow for changing arrow density

[themusicgod1]

Imagine trying to model a non-linear system with two critical points (maybe they are close to eachother, maybe they aren't) where you know the region of the critical points but you are not sure the behaviour of those critical points and want to verify your knowledge of said behaviour. You're going to want to have a couple of isoclines,which you can already do, but you also might want more than the 196-225 arrows that, while probably a decent amount of arrows for some purposes, don't give a very clear idea of which direction for very small regions between critical points.

This change adds a new value, that you can configure in plot setup, called number_of_arrows, which is roughly going to correspond to how many arrows are displayed. If you leave it default, it gives roughly the number of arrows, but you can crank it way up. That way you can get a better idea of these systems, like say,
x'=x-y+x^2
y'=x+2*y
where you want to see the swirl of the arrows a in little more detail

to review, to get to this screen, you go

1) load ("plotdf");
2) plotdf(x,[x,-1,1],[y,-1,1]);
(or substitute for the first 'x' your favourite defined function f(x,y), and for the two ranges, your own chosen range)
3) click on the wrench icon to go into Plot Setup

before the change:
4) nothing, you're SOL there is no setting for number of arrows

after the change:
4) Enter in a chosen number of arrows to display
5) click OK
6) click the refresh icon to generate a new phase diagram/slope field, and optionally click on said diagram to plot an isocline.

xmaxima:
  Installed: 5.37.2-8
  Candidate: 5.37.2-8
  Version table:
 *** 5.37.2-8 500
        500 http://archive.ubuntu.com/ubuntu yakkety/universe amd64 Packages
        100 /var/lib/dpkg/status

maxima:
  Installed: 5.37.2-8
  Candidate: 5.37.2-8
  Version table:
 *** 5.37.2-8 500
        500 http://archive.ubuntu.com/ubuntu yakkety/universe amd64 Packages
        100 /var/lib/dpkg/status

Ubuntu: 16.10 (yakkety)

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: xmaxima 5.37.2-8
ProcVersionSignature: Ubuntu 4.8.0-39.42-generic 4.8.17
Uname: Linux 4.8.0-39-generic x86_64
ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Mar 5 15:37:12 2017
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-07-09 (970 days ago)
InstallationMedia: Ubuntu-GNOME 14.10 "Utopic Unicorn" - Alpha amd64 (20140708)
SourcePackage: maxima
UpgradeStatus: Upgraded to yakkety on 2016-10-16 (140 days ago)

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "adds new field, number_of_arrows which controls plotdf arrow density" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[PeterPall (peterpall)]

I have committed your patch to maxima's repository at maxima.sourceforge.net as Commit #dca80e35f8f5e7e2eb91498ec3692cafa3f781f6 => it will be officially included in the next maxima version which will take place in April. Thanks a lot! - and kind regards,
   Gunter.