xrandr Size 1920x1080 not found in available modes ubuntu - bash

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?

Answer 1

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.