xrandr Size 1920x1080 not found in available modes ubuntu

Question

I'm using a Dell XPS 15 9550 with 4k display and ubuntu as OS. I need to use Matlab but I have (as always) an HighDPI issue. Currently I'm using r2017a version of Matlab.

To solve this problem I'm trying to use a little script to avoid the problem:

Myscript.sh

#!/bin/sh

#set scaling to x1.0 to remove the zoom used in HDPI screens
gsettings set org.gnome.desktop.interface scaling-factor 1
#Used in ubuntu machines
gsettings set com.ubuntu.user-interface scale-factor "{'HDMI1': 8, 'eDP1': 8}"
#applying full HD resolution
xrandr -s 1920x1080
# call your program
/usr/local/MATLAB/R2017a/bin/matlab
#wait for the process to terminate
wait
#now coming back to the original screen resolution and scaling
# set scaling to x2.0
gsettings set org.gnome.desktop.interface scaling-factor 2
#same as before
gsettings set com.ubuntu.user-interface scale-factor "{'HDMI1': 8, 'eDP1': 16}"
#back to original resolution
xrandr -s 3840x2160

When I launch it I receive this error from console:

"Size 1920x1080 not found in available modes"

So I've done:

cvt 1920 1080 60

Output:

# 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz
Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

After that:

xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

and finally

xrandr --addmode eDP-1-1 1920x1080

I've found eDP-1-1 using xrandr -q. Here the output

Screen 0: minimum 8 x 8, current 3840 x 2160, maximum 16384 x 16384
eDP-1-1 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 346mm x 194mm
  3840x2160     60.00*+
   2048x1536     60.00  
   1920x1440     60.00  
   1856x1392     60.01  
   1792x1344     60.01  
   1920x1200     59.95  
   1920x1080     59.93  
   1600x1200     60.00  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1360x768      59.80    59.96  
   1152x864      60.00  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   960x600       60.00  
   960x540       59.99  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   800x512       60.17  
   700x525       59.98  
   640x512       60.02  
   720x450       59.89  
   640x480       60.00    59.94  
   680x384       59.80    59.96  
   576x432       60.06  
   512x384       60.00  
   400x300       60.32    56.34  
   320x240       60.05  
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-2 disconnected (normal left inverted right x axis y axis)
HDMI-1-2 disconnected (normal left inverted right x axis y axis)

So I think I've done all things right, but still script doesn't work and console still give me the same error.

I'm done something wrong?

Solution

I had the same problem with my 4k screen. I did all the steps you described but instead of:

#applying full HD resolution
xrandr -s 1920x1080

I used this:

xrandr --output eDP-1-1 --mode 1920x1080

and it worked flawlessly.

Also, if you only have troubles in Matlab with your 4k screen, you can consider changing the scaling within Matlab by typing the following commands in the Matlab terminal:

s = settings;s.matlab.desktop.DisplayScaleFactor
s.matlab.desktop.DisplayScaleFactor.PersonalValue = 2

This setting will only take effect after matlab is restarted.

My main source for HiDPI screens in linux is Archwiki. They provide clear detailed information.