Alternative function to pwelch() and different results

I use the pwelch() function from the DSP Toolbox in Matlab R2017a to calculate the power spectral density of a given vector. It works very nice, but now I need to run my code on a Matlab installation which do not have the DSP Toolbox so I need to find an alternative function.

I've found this function with source code: pwelch from Octave which runs on Matlab without problems.

The only this is that the pwelch function from DSP Toolbox returns an output vector which is different from the pwelch from Octave since it has a different size and also different values.

Can you please help me to find a solution to my problem? I already looked on Matlab file exchange but I wasn't able to find a similar function.

This is the original vector:

I_sx(570:970)
ans =
  -27.3980
  -27.3590
  -27.2351
  -27.0177
  -26.9524
  -26.7875
  -26.6448
  -26.5835
  -26.5095
  -26.4065
  -26.5041
  -26.5189
  -26.4785
  -26.5424
  -26.5155
  -26.3964
  -26.4139
  -26.3351
  -26.3405
  -26.3903
  -26.3775
  -26.3405
  -26.3445
  -26.2617
  -26.2032
  -26.1924
  -26.2631
  -26.2025
  -26.2658
  -26.2678
  -26.2375
  -26.2321
  -26.2429
  -26.1365
  -26.1210
  -26.0638
  -26.0497
  -26.1244
  -26.1426
  -26.0477
  -26.0672
  -26.0840
  -26.0820
  -26.0712
  -26.1385
  -26.0726
  -26.1843
  -26.2133
  -26.2826
  -26.3587
  -26.4253
  -26.3452
  -26.4031
  -26.3836
  -26.3910
  -26.4354
  -26.4092
  -26.3142
  -26.3284
  -26.2456
  -26.1412
  -26.0860
  -26.1163
  -26.0645
  -26.1069
  -26.1332
  -26.1527
  -26.1136
  -26.1722
  -26.0382
  -26.0261
  -26.0255
  -26.0012
  -25.9177
  -25.9965
  -25.9379
  -25.9662
  -25.9177
  -25.8625
  -25.8430
  -25.8969
  -25.8282
  -25.8390
  -25.8612
  -25.8625
  -25.8592
  -25.9090
  -25.7750
  -25.7831
  -25.7420
  -25.7017
  -25.6983
  -25.7447
  -25.6478
  -25.5798
  -25.5340
  -25.4384
  -25.4526
  -25.4640
  -25.4095
  -25.3274
  -25.3772
  -25.4526
  -25.4452
  -25.5159
  -25.4533
  -25.4263
  -25.4829
  -25.5219
  -25.5717
  -25.6916
  -25.7252
  -25.6922
  -25.7414
  -25.7501
  -25.6801
  -25.7070
  -25.6417
  -25.6290
  -25.6996
  -25.6996
  -25.6909
  -25.7407
  -25.6323
  -25.5623
  -25.5872
  -25.5616
  -25.6040
  -25.6929
  -25.6619
  -25.6579
  -25.7077
  -25.6835
  -25.6727
  -25.7892
  -25.8706
  -25.8679
  -25.9925
  -26.0685
  -26.1433
  -26.2550
  -26.3116
  -26.2698
  -26.2617
  -26.2240
  -26.2173
  -26.2678
  -26.3910
  -26.2900
  -26.2725
  -26.2739
  -26.3028
  -26.3439
  -26.4415
  -26.4112
  -26.4751
  -26.5532
  -26.5613
  -26.6461
  -26.6502
  -26.6239
  -26.6286
  -26.6367
  -26.6946
  -26.7606
  -26.8245
  -26.7821
  -26.7942
  -26.7639
  -26.7410
  -26.7511
  -26.7801
  -26.7229
  -26.7390
  -26.7249
  -26.6683
  -26.6259
  -26.6461
  -26.5337
  -26.4960
  -26.4610
  -26.4644
  -26.4671
  -26.5620
  -26.4920
  -26.4920
  -26.4018
  -26.3735
  -26.2402
  -26.3095
  -26.2739
  -26.2052
  -26.1608
  -26.1325
  -26.0719
  -26.0914
  -26.0228
  -26.0483
  -26.0732
  -26.0840
  -26.0840
  -26.1372
  -26.1318
  -26.1554
  -26.0968
  -26.1096
  -26.0813
  -26.2025
  -26.1944
  -26.2072
  -26.2658
  -26.2813
  -26.2584
  -26.2873
  -26.2065
  -26.2187
  -26.2388
  -26.2866
  -26.2860
  -26.3822
  -26.3896
  -26.4159
  -26.3843
  -26.3661
  -26.3176
  -26.3721
  -26.3210
  -26.3923
  -26.4596
  -26.4724
  -26.4637
  -26.5155
  -26.4496
  -26.4623
  -26.4267
  -26.4341
  -26.4206
  -26.4226
  -26.2880
  -26.2267
  -26.1325
  -26.0867
  -25.9884
  -26.0154
  -25.9534
  -25.9541
  -25.9400
  -25.9352
  -25.8592
  -25.8996
  -25.8174
  -25.7999
  -25.7596
  -25.7878
  -25.7771
  -25.8040
  -25.7528
  -25.7151
  -25.6512
  -25.5616
  -25.4708
  -25.4694
  -25.3530
  -25.3280
  -25.3240
  -25.3388
  -25.3583
  -25.4203
  -25.3395
  -25.3213
  -25.3153
  -25.3381
  -25.3045
  -25.3065
  -25.2311
  -25.2506
  -25.1524
  -25.0972
  -25.1497
  -25.2998
  -25.3597
  -25.4755
  -25.5515
  -25.6518
  -25.6868
  -25.7313
  -25.7165
  -25.8195
  -25.8403
  -25.9218
  -25.9346
  -26.0928
  -26.0308
  -26.1372
  -26.1345
  -26.1695
  -26.2301
  -26.3216
  -26.3304
  -26.4583
  -26.5431
  -26.6320
  -26.6576
  -26.7794
  -26.8009
  -26.8723
  -26.8770
  -26.9315
  -26.9214
  -26.9753
  -26.9181
  -26.9376
  -26.8131
  -26.7599
  -26.8178
  -26.9376
  -26.9571
  -27.0534
  -27.0998
  -27.1362
  -27.0992
  -27.0897
  -26.9834
  -27.0157
  -26.9430
  -26.9686
  -26.9807
  -27.0318
  -26.9396
  -26.9665
  -26.8434
  -26.7760
  -26.6764
  -26.7309
  -26.6333
  -26.6838
  -26.6589
  -26.7121
  -26.7202
  -26.7525
  -26.6441
  -26.6333
  -26.5835
  -26.6461
  -26.6077
  -26.5896
  -26.4960
  -26.5337
  -26.3937
  -26.3856
  -26.3728
  -26.3964
  -26.4166
  -26.4327
  -26.4038
  -26.3674
  -26.2638
  -26.1534
  -26.0658
  -26.0510
  -26.0483
  -26.0389
  -25.9810
  -26.0443
  -25.9851
  -25.9770
  -25.9198
  -25.8700
  -25.8531
  -25.8686
  -25.8625
  -25.9036
  -25.9958
  -26.0881
  -26.0773
  -26.1022
  -26.0894
  -26.1237
  -26.1534
  -26.1951
  -26.2112
  -26.2590
  -26.3176
  -26.3519
  -26.3089
  -26.3755
  -26.4469
  -26.5849
  -26.6205
  -26.6973
  -26.7612
  -26.8380
  -26.8508
  -26.8487
  -26.9840
  -27.0467
  -27.1140
  -27.1712
  -27.2224
  -27.2526
  -27.2513

and this is the output of the pwelch() from DSP:

pxx_sx = pwelch(I_sx(570:970))
pxx_sx = 7043.99509673063
11644.5569003827
6455.19574077649
2247.33527612618
418.419085520639
25.8716525803097
0.241379153886240
0.219727631954535
0.0360675641941806
0.173566460147319
0.682167747712714
0.190180572625892
0.241387363165533
0.717710297747080
0.0866891794491317
0.371595110033528
0.701651401197791
0.0512352870193891
0.325757317891398
0.482422466203071
0.0115310246339952
0.334947330162198
0.347560433417062
0.00280910319719409
0.316868381840343
0.225217005806746
0.0186647932806373
0.376906354397266
0.238889516785153
0.00521936600798125
0.204174373656829
0.0786629204881135
0.0493182418041582
0.244324909727162
0.0630841760289611
0.0563107092331113
0.201165066521218
0.0319585032915665
0.0715995112815609
0.165911442308514
0.0122886724952156
0.0913135383951907
0.144961117009115
0.00469552565159905
0.0968991607335580
0.114738979042298
0.000505215232955028
0.0966866310150594
0.0823152225662298
0.00243009108059338
0.104166781848088
0.0634777517797514
0.00666177945439951
0.0995154150079024
0.0426500956153844
0.0145800246291918
0.0959121054451539
0.0274492499099761
0.0229864020361143
0.0883757712175194
0.0152532188182601
0.0327542962407699
0.0816271279390272
0.00777137516045686
0.0385332496733992
0.0679758425283955
0.00202707963479403
0.0471411396932288
0.0581699428371817
0.000207291419450440
0.0528221810897814
0.0475603504208714
0.000751877198188671
0.0551577345467582
0.0354173432458632
0.00372689980530504
0.0584637590792945
0.0267477617881123
0.00774031903310985
0.0565400237516173
0.0167298714937103
0.0146331798893914
0.0595470898355228
0.0138831156719556
0.0177088273429665
0.0477107528839032
0.00498651459720749
0.0284675925501540
0.0485273944246418
0.00195300450019559
0.0308046011266940
0.0401163066002232
0.000229547969600012
0.0364595843705069
0.0341250622584901
0.000364516846922977
0.0392477940022582
0.0263325987849415
0.00251536053243924
0.0429717038191161
0.0204531354326404
0.00547838894213586
0.0433747165479543
0.0140023083216393
0.00962969639786918
0.0424867822504836
0.00823527585224237
0.0152341250389282
0.0422302161901552
0.00471932515219331
0.0194736022464636
0.0377128344847568
0.00152511955516697
0.0256015990238373
0.0346070179924435
0.000274637418489702
0.0302501257091915
0.0299752943114966
0.000200085803745744
0.0327878546068529
0.0228968159826973
0.00205932069608192
0.0380893602848498
0.0188869996392939
0.00477588222203371
0.0402211356410538
0.0152309990724466
0.0105211012506845
0.0208092769955709

while this other one is the result from the pwelch() source code found from Octave:

pxx_sx_t = pwelch_r(I_sx(570:970))
3.70288869240553
2.20826281343221
0.0764382850559608
0.0254604504720041
0.0160990668784325
0.00447434006158207
0.00296399977959586
0.00162247506448442
0.00157682669543061
0.000860528976692023
0.00328820318575463
0.00378052742157819
0.00100836667971670
0.000549872960056774
0.000724331781856895
0.00165392374757721
0.00389279055274153

[marcusbarnet]

I tried to find out a solution, but I wasn't able to find anything so far :( Hope someone can help!