error: d:\download\D:\Downloads\Octave_ex: Invalid argument

[patpin]

I am running this code ex2_reg.m
<https://octave.1599824.n4.nabble.com/file/t373649/ex2_reg.m>  
 and have strange behaviour of the command window of Octave 5.2.0. 
When I do not put a break in fminunc but at the line calling the function
the command window very brieflys shows stopped at … and clears its screen an
restarts the ex2_reg.m script. When I put a break in the fminunc function
itself I get this on my screen (see below). I am running Octave from my C:
drive but the message refers to the D: where my windows installer file is.
Before running the script I give the correct cd … instruction in the command
window to the map with the script and the data and functions. (also on D:
but not in D:\downloads. Other scripts function as it should. Somebody can
help. 

Cost at initial theta (zeros): 0.693147
Expected cost (approx): 0.693
Gradient at initial theta (zeros) - first five values only:
 0.008475
 0.018788
 0.000078
 0.050345
 0.011501
Expected gradients (approx) - first five values only:
 0.0085
 0.0188
 0.0001
 0.0503
 0.0115

Program paused00. Press enter to continue.

Cost at test theta (with lambda = 10): 3.164509
Expected cost (approx): 3.16
Gradient at test theta - first five values only:
 0.346045
 0.161352
 0.194796
 0.226863
 0.092186
Expected gradients (approx) - first five values only:
 0.3460
 0.1614
 0.1948
 0.2269
 0.0922

Program paused10. Press enter to continue.

Program paused101. Press enter to continue.

Program paused102. Press enter to continue.

Program paused103. Press enter to continue.
stopped in
D:\DATA-MEDION\beurs\VerhelleMTI\upscfeverCursus\logistischEX2\ex2_reg.m
at line 127
127: [theta, J, exit_flag] = fminunc(@(t)(costFunctionReg(t, X, y, lambda)),
initial
_theta, options);
debug>
debug> x0
x0 =

   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0
   0

debug>
Program paused11. Press enter to continue.

Program paused12. Press enter to continue.
Train Accuracy: 83.050847
Expected accuracy (with lambda = 1): 83.1 (approx)
error: 'x0' undefined near line 1 column 1
error: called from
    ex2_reg at line 127 column 23
debug> cd d:\download\D:\Downloads\Octave_ex
error: d:\download\D:\Downloads\Octave_ex: Invalid argument
error: called from
    ex2_reg at line 127 column 23
error: d:\download\D:\Downloads\Octave_ex: Invalid argument
error: called from
    ex2_reg at line 127 column 23
debug>   (<<< here I press enter and same problem continues)
error: d:\download\D:\Downloads\Octave_ex: Invalid argument
error: called from
    ex2_reg at line 127 column 23
debug>
(here I can still ask for e.g. X and it is shown)(after  pressing type
'return' nothing happens anymore..  until I press F5 and get)
error: element number 1 undefined in return list
error: called from
    ex2_reg at line 127 column 23
>>




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