Why are lines missing with linespoints plotting style?

Question

I'm trying to plot 3 graphs from 3 data files, which I produced from cpp code. The 3 graphs are respectively the position, speed and acceleration of a pendulum. Here is my code:

set key font ",16"
set title "Evolution d'un pendule en fonction du temps"
plot for [i=2:4] 'data/pendulum.md' u 1:i w linesp title "θ(t) " . (i-2)

But for some reason linesp doesn't produce lines, only points. I tried with less points but still doesn't work. Now, with other functions and simulations, the linesp works fine. Maybe the [i=2:4] prevents gnuplot from producing lines. I have literraly no idea and any help is welcome. Here are my graphs and data:

0.01000 0.39809 -0.19101 -18.77588 #t θ θdot θddot

0.02000 0.39430 -0.37877 -18.36979 #t θ θdot θddot

0.03000 0.38868 -0.56247 -17.88515 #t θ θdot θddot

0.04000 0.38126 -0.74132 -17.32458 #t θ θdot θddot

0.05000 0.37212 -0.91456 -16.69088 #t θ θdot θddot

0.06000 0.36130 -1.08147 -15.98706 #t θ θdot θddot

0.07000 0.34889 -1.24134 -15.21633 #t θ θdot θddot

0.08000 0.33496 -1.39351 -14.38218 #t θ θdot θddot

0.09000 0.31958 -1.53733 -13.48838 #t θ θdot θddot

0.10000 0.30286 -1.67221 -12.53896 #t θ θdot θddot

0.11000 0.28488 -1.79760 -11.53832 #t θ θdot θddot

0.12000 0.26575 -1.91298 -10.49112 #t θ θdot θddot

0.13000 0.24558 -2.01790 -9.40239 #t θ θdot θddot

0.14000 0.22446 -2.11192 -8.27746 #t θ θdot θddot

0.15000 0.20251 -2.19469 -7.12195 #t θ θdot θddot

0.16000 0.17985 -2.26591 -5.94177 #t θ θdot θddot

0.17000 0.15660 -2.32533 -4.74305 #t θ θdot θddot

0.18000 0.13287 -2.37276 -3.53212 #t θ θdot θddot

0.19000 0.10879 -2.40808 -2.31544 #t θ θdot θddot

0.20000 0.08448 -2.43124 -1.09957 #t θ θdot θddot

0.21000 0.06005 -2.44223 0.10894 #t θ θdot θddot

0.22000 0.03564 -2.44114 1.30356 #t θ θdot θddot

0.23000 0.01136 -2.42811 2.47789 #t θ θdot θddot

0.24000 -0.01267 -2.40333 3.62572 #t θ θdot θddot

0.25000 -0.03634 -2.36707 4.74107 #t θ θdot θddot

0.26000 -0.05954 -2.31966 5.81827 #t θ θdot θddot

0.27000 -0.08215 -2.26148 6.85199 #t θ θdot θddot

0.28000 -0.10408 -2.19296 7.83731 #t θ θdot θddot

0.29000 -0.12523 -2.11459 8.76972 #t θ θdot θddot

0.30000 -0.14550 -2.02689 9.64517 #t θ θdot θddot

0.31000 -0.16480 -1.93044 10.46010 #t θ θdot θddot

0.32000 -0.18306 -1.82584 11.21139 #t θ θdot θddot

0.33000 -0.20020 -1.71372 11.89644 #t θ θdot θddot

0.34000 -0.21615 -1.59476 12.51306 #t θ θdot θddot

0.35000 -0.23084 -1.46963 13.05957 #t θ θdot θddot

0.36000 -0.24423 -1.33903 13.53467 #t θ θdot θddot

0.37000 -0.25627 -1.20368 13.93750 #t θ θdot θddot

0.38000 -0.26691 -1.06431 14.26756 #t θ θdot θddot

0.39000 -0.27613 -0.92163 14.52472 #t θ θdot θddot

0.40000 -0.28389 -0.77639 14.70914 #t θ θdot θddot

0.41000 -0.29019 -0.62930 14.82132 #t θ θdot θddot

0.42000 -0.29500 -0.48108 14.86199 #t θ θdot θddot

0.43000 -0.29832 -0.33246 14.83217 #t θ θdot θddot

0.44000 -0.30016 -0.18414 14.73307 #t θ θdot θddot

0.45000 -0.30053 -0.03681 14.56616 #t θ θdot θddot

0.46000 -0.29944 0.10885 14.33307 #t θ θdot θddot

0.47000 -0.29692 0.25218 14.03567 #t θ θdot θddot

0.48000 -0.29300 0.39254 13.67600 #t θ θdot θddot

0.49000 -0.28770 0.52930 13.25630 #t θ θdot θddot

0.50000 -0.28108 0.66186 12.77899 #t θ θdot θddot

0.51000 -0.27319 0.78965 12.24671 #t θ θdot θddot

0.52000 -0.26407 0.91212 11.66228 #t θ θdot θddot

0.53000 -0.25378 1.02874 11.02872 #t θ θdot θddot

0.54000 -0.24239 1.13903 10.34928 #t θ θdot θddot

0.55000 -0.22996 1.24252 9.62738 #t θ θdot θddot

0.56000 -0.21658 1.33880 8.86666 #t θ θdot θddot

0.57000 -0.20230 1.42746 8.07096 #t θ θdot θddot

0.58000 -0.18722 1.50817 7.24431 #t θ θdot θddot

0.59000 -0.17141 1.58061 6.39090 #t θ θdot θddot

0.60000 -0.15497 1.64452 5.51510 #t θ θdot θddot

0.61000 -0.13797 1.69967 4.62141 #t θ θdot θddot

0.62000 -0.12051 1.74589 3.71444 #t θ θdot θddot

0.63000 -0.10268 1.78303 2.79888 #t θ θdot θddot

0.64000 -0.08457 1.81102 1.87949 #t θ θdot θddot

0.65000 -0.06627 1.82982 0.96104 #t θ θdot θddot

0.66000 -0.04788 1.83943 0.04827 #t θ θdot θddot

0.67000 -0.02948 1.83991 -0.85412 #t θ θdot θddot

0.68000 -0.01117 1.83137 -1.74154 #t θ θdot θddot

0.69000 0.00697 1.81395 -2.60950 #t θ θdot θddot

0.70000 0.02485 1.78786 -3.45370 #t θ θdot θddot

0.71000 0.04239 1.75332 -4.27004 #t θ θdot θddot

0.72000 0.05949 1.71062 -5.05462 #t θ θdot θddot

0.73000 0.07609 1.66008 -5.80383 #t θ θdot θddot

0.74000 0.09211 1.60204 -6.51429 #t θ θdot θddot

0.75000 0.10748 1.53689 -7.18295 #t θ θdot θddot

0.76000 0.12213 1.46506 -7.80704 #t θ θdot θddot

0.77000 0.13600 1.38699 -8.38411 #t θ θdot θddot

0.78000 0.14903 1.30315 -8.91202 #t θ θdot θddot

0.79000 0.16117 1.21403 -9.38895 #t θ θdot θddot

0.80000 0.17238 1.12014 -9.81339 #t θ θdot θddot

0.81000 0.18260 1.02201 -10.18414 #t θ θdot θddot

0.82000 0.19180 0.92017 -10.50030 #t θ θdot θddot

0.83000 0.19995 0.81516 -10.76124 #t θ θdot θddot

0.84000 0.20702 0.70755 -10.96661 #t θ θdot θddot

0.85000 0.21300 0.59789 -11.11635 #t θ θdot θddot

0.86000 0.21787 0.48672 -11.21061 #t θ θdot θddot

0.87000 0.22162 0.37462 -11.24981 #t θ θdot θddot

0.88000 0.22424 0.26212 -11.23458 #t θ θdot θddot

0.89000 0.22574 0.14977 -11.16576 #t θ θdot θddot

0.90000 0.22612 0.03812 -11.04441 #t θ θdot θddot

0.91000 0.22539 -0.07233 -10.87177 #t θ θdot θddot

0.92000 0.22358 -0.18105 -10.64930 #t θ θdot θddot

0.93000 0.22071 -0.28754 -10.37861 #t θ θdot θddot

0.94000 0.21679 -0.39133 -10.06151 #t θ θdot θddot

0.95000 0.21188 -0.49194 -9.69996 #t θ θdot θddot

0.96000 0.20599 -0.58894 -9.29612 #t θ θdot θddot

0.97000 0.19917 -0.68190 -8.85229 #t θ θdot θddot

0.98000 0.19146 -0.77042 -8.37093 #t θ θdot θddot

0.99000 0.18292 -0.85413 -7.85466 #t θ θdot θddot

1.00000 0.17359 -0.93268 -7.30625 #t θ θdot θddot

1.01000 0.16354 -1.00574 -6.72859 #t θ θdot θddot

1.02000 0.15281 -1.07303 -6.12474 #t θ θdot θddot

1.03000 0.14146 -1.13428 -5.49783 #t θ θdot θddot

1.04000 0.12957 -1.18925 -4.85113 #t θ θdot θddot

1.05000 0.11719 -1.23777 -4.18799 #t θ θdot θddot

1.06000 0.10440 -1.27965 -3.51182 #t θ θdot θddot

1.07000 0.09125 -1.31476 -2.82612 #t θ θdot θddot

1.08000 0.07782 -1.34303 -2.13440 #t θ θdot θddot

1.09000 0.06418 -1.36437 -1.44019 #t θ θdot θddot

1.10000 0.05039 -1.37877 -0.74701 #t θ θdot θddot

1.11000 0.03653 -1.38624 -0.05837 #t θ θdot θddot

1.12000 0.02266 -1.38682 0.62229 #t θ θdot θddot

1.13000 0.00885 -1.38060 1.29161 #t θ θdot θddot

1.14000 -0.00483 -1.36769 1.94631 #t θ θdot θddot

1.15000 -0.01831 -1.34822 2.58323 #t θ θdot θddot

1.16000 -0.03153 -1.32239 3.19937 #t θ θdot θddot

1.17000 -0.04444 -1.29040 3.79186 #t θ θdot θddot

1.18000 -0.05696 -1.25248 4.35801 #t θ θdot θddot

1.19000 -0.06905 -1.20890 4.89531 #t θ θdot θddot

1.20000 -0.08065 -1.15994 5.40148 #t θ θdot θddot

1.21000 -0.09171 -1.10593 5.87440 #t θ θdot θddot

1.22000 -0.10218 -1.04719 6.31221 #t θ θdot θddot

1.23000 -0.11202 -0.98406 6.71322 #t θ θdot θddot

1.24000 -0.12119 -0.91693 7.07600 #t θ θdot θddot

1.25000 -0.12965 -0.84617 7.39934 #t θ θdot θddot

1.26000 -0.13737 -0.77218 7.68223 #t θ θdot θddot

1.27000 -0.14433 -0.69536 7.92389 #t θ θdot θddot

1.28000 -0.15049 -0.61612 8.12377 #t θ θdot θddot

1.29000 -0.15584 -0.53488 8.28151 #t θ θdot θddot

1.30000 -0.16036 -0.45206 8.39697 #t θ θdot θddot

1.31000 -0.16404 -0.36809 8.47018 #t θ θdot θddot

1.32000 -0.16687 -0.28339 8.50141 #t θ θdot θddot

1.33000 -0.16886 -0.19838 8.49108 #t θ θdot θddot

1.34000 -0.16999 -0.11347 8.43980 #t θ θdot θddot

1.35000 -0.17028 -0.02907 8.34836 #t θ θdot θddot

1.36000 -0.16974 0.05441 8.21770 #t θ θdot θddot

1.37000 -0.16837 0.13659 8.04893 #t θ θdot θddot

1.38000 -0.16620 0.21708 7.84333 #t θ θdot θddot

1.39000 -0.16325 0.29551 7.60230 #t θ θdot θddot

1.40000 -0.15953 0.37154 7.32740 #t θ θdot θddot

1.41000 -0.15508 0.44481 7.02033 #t θ θdot θddot

1.42000 -0.14993 0.51501 6.68289 #t θ θdot θddot

1.43000 -0.14411 0.58184 6.31704 #t θ θdot θddot

1.44000 -0.13766 0.64501 5.92483 #t θ θdot θddot

1.45000 -0.13062 0.70426 5.50844 #t θ θdot θddot

1.46000 -0.12303 0.75935 5.07011 #t θ θdot θddot

1.47000 -0.11493 0.81005 4.61222 #t θ θdot θddot

1.48000 -0.10637 0.85617 4.13719 #t θ θdot θddot

1.49000 -0.09739 0.89754 3.64751 #t θ θdot θddot

1.50000 -0.08805 0.93402 3.14575 #t θ θdot θddot

1.51000 -0.07840 0.96547 2.63451 #t θ θdot θddot

1.52000 -0.06848 0.99182 2.11640 #t θ θdot θddot

1.53000 -0.05835 1.01298 1.59408 #t θ θdot θddot

1.54000 -0.04806 1.02892 1.07018 #t θ θdot θddot

1.55000 -0.03766 1.03963 0.54734 #t θ θdot θddot

1.56000 -0.02721 1.04510 0.02815 #t θ θdot θddot

1.57000 -0.01676 1.04538 -0.48484 #t θ θdot θddot

1.58000 -0.00635 1.04053 -0.98912 #t θ θdot θddot

1.59000 0.00395 1.03064 -1.48228 #t θ θdot θddot

1.60000 0.01411 1.01582 -1.96199 #t θ θdot θddot

1.61000 0.02407 0.99620 -2.42601 #t θ θdot θddot

1.62000 0.03379 0.97194 -2.87222 #t θ θdot θddot

1.63000 0.04323 0.94322 -3.29862 #t θ θdot θddot

1.64000 0.05233 0.91023 -3.70334 #t θ θdot θddot

1.65000 0.06106 0.87320 -4.08466 #t θ θdot θddot

1.66000 0.06938 0.83235 -4.44100 #t θ θdot θddot

1.67000 0.07726 0.78794 -4.77093 #t θ θdot θddot

1.68000 0.08467 0.74023 -5.07319 #t θ θdot θddot

1.69000 0.09156 0.68950 -5.34666 #t θ θdot θddot

1.70000 0.09792 0.63603 -5.59040 #t θ θdot θddot

1.71000 0.10372 0.58013 -5.80363 #t θ θdot θddot

1.72000 0.10894 0.52209 -5.98572 #t θ θdot θddot

1.73000 0.11357 0.46223 -6.13623 #t θ θdot θddot

1.74000 0.11757 0.40087 -6.25484 #t θ θdot θddot

1.75000 0.12096 0.33832 -6.34142 #t θ θdot θddot

1.76000 0.12371 0.27491 -6.39599 #t θ θdot θddot

1.77000 0.12582 0.21095 -6.41870 #t θ θdot θddot

1.78000 0.12728 0.14676 -6.40988 #t θ θdot θddot

1.79000 0.12811 0.08266 -6.36997 #t θ θdot θddot

1.80000 0.12830 0.01896 -6.29958 #t θ θdot θddot

1.81000 0.12786 -0.04403 -6.19941 #t θ θdot θddot

1.82000 0.12680 -0.10603 -6.07033 #t θ θdot θddot

1.83000 0.12513 -0.16673 -5.91332 #t θ θdot θddot

1.84000 0.12287 -0.22586 -5.72947 #t θ θdot θddot

1.85000 0.12004 -0.28316 -5.51998 #t θ θdot θddot

1.86000 0.11666 -0.33836 -5.28618 #t θ θdot θddot

1.87000 0.11275 -0.39122 -5.02947 #t θ θdot θddot

1.88000 0.10833 -0.44151 -4.75136 #t θ θdot θddot

1.89000 0.10344 -0.48903 -4.45345 #t θ θdot θddot

1.90000 0.09811 -0.53356 -4.13739 #t θ θdot θddot

1.91000 0.09236 -0.57494 -3.80495 #t θ θdot θddot

1.92000 0.08623 -0.61299 -3.45792 #t θ θdot θddot

1.93000 0.07975 -0.64756 -3.09816 #t θ θdot θddot

1.94000 0.07296 -0.67855 -2.72757 #t θ θdot θddot

1.95000 0.06591 -0.70582 -2.34811 #t θ θdot θddot

1.96000 0.05861 -0.72930 -1.96173 #t θ θdot θddot

1.97000 0.05112 -0.74892 -1.57041 #t θ θdot θddot

1.98000 0.04348 -0.76462 -1.17615 #t θ θdot θddot

1.99000 0.03571 -0.77639 -0.78093 #t θ θdot θddot

2.00000 0.02787 -0.78420 -0.38672 #t θ θdot θddot

2.01000 0.01999 -0.78806 0.00455 #t θ θdot θddot

2.02000 0.01211 -0.78802 0.39096 #t θ θdot θddot

2.03000 0.00427 -0.78411 0.77066 #t θ θdot θddot

2.04000 -0.00349 -0.77640 1.14185 #t θ θdot θddot

2.05000 -0.01114 -0.76498 1.50279 #t θ θdot θddot

2.06000 -0.01864 -0.74995 1.85182 #t θ θdot θddot

2.07000 -0.02596 -0.73144 2.18735 #t θ θdot θddot

2.08000 -0.03305 -0.70956 2.50790 #t θ θdot θddot

2.09000 -0.03990 -0.68448 2.81207 #t θ θdot θddot

2.10000 -0.04646 -0.65636 3.09856 #t θ θdot θddot

2.11000 -0.05272 -0.62538 3.36620 #t θ θdot θddot

2.12000 -0.05863 -0.59172 3.61391 #t θ θdot θddot

2.13000 -0.06419 -0.55558 3.84073 #t θ θdot θddot

2.14000 -0.06936 -0.51717 4.04583 #t θ θdot θddot

2.15000 -0.07413 -0.47671 4.22848 #t θ θdot θddot

2.16000 -0.07847 -0.43443 4.38809 #t θ θdot θddot

2.17000 -0.08238 -0.39055 4.52418 #t θ θdot θddot

2.18000 -0.08583 -0.34530 4.63640 #t θ θdot θddot

2.19000 -0.08882 -0.29894 4.72452 #t θ θdot θddot

2.20000 -0.09134 -0.25169 4.78841 #t θ θdot θddot

2.21000 -0.09337 -0.20381 4.82810 #t θ θdot θddot

2.22000 -0.09493 -0.15553 4.84370 #t θ θdot θddot

2.23000 -0.09600 -0.10709 4.83544 #t θ θdot θddot

2.24000 -0.09659 -0.05874 4.80368 #t θ θdot θddot

2.25000 -0.09669 -0.01070 4.74886 #t θ θdot θddot

2.26000 -0.09633 0.03679 4.67153 #t θ θdot θddot

2.27000 -0.09549 0.08350 4.57237 #t θ θdot θddot

2.28000 -0.09420 0.12923 4.45211 #t θ θdot θddot

2.29000 -0.09246 0.17375 4.31161 #t θ θdot θddot

2.30000 -0.09029 0.21686 4.15179 #t θ θdot θddot

2.31000 -0.08771 0.25838 3.97366 #t θ θdot θddot

2.32000 -0.08473 0.29812 3.77830 #t θ θdot θddot

2.33000 -0.08137 0.33590 3.56688 #t θ θdot θddot

2.34000 -0.07765 0.37157 3.34062 #t θ θdot θddot

2.35000 -0.07360 0.40498 3.10078 #t θ θdot θddot

2.36000 -0.06924 0.43598 2.84872 #t θ θdot θddot

2.37000 -0.06460 0.46447 2.58580 #t θ θdot θddot

2.38000 -0.05970 0.49033 2.31343 #t θ θdot θddot

2.39000 -0.05456 0.51346 2.03307 #t θ θdot θddot

2.40000 -0.04922 0.53379 1.74619 #t θ θdot θddot

2.41000 -0.04371 0.55126 1.45426 #t θ θdot θddot

2.42000 -0.03805 0.56580 1.15879 #t θ θdot θddot

2.43000 -0.03228 0.57739 0.86127 #t θ θdot θddot

2.44000 -0.02642 0.58600 0.56320 #t θ θdot θddot

2.45000 -0.02050 0.59163 0.26604 #t θ θdot θddot

2.46000 -0.01456 0.59429 -0.02874 #t θ θdot θddot

2.47000 -0.00862 0.59400 -0.31972 #t θ θdot θddot

2.48000 -0.00271 0.59081 -0.60551 #t θ θdot θddot

2.49000 0.00314 0.58475 -0.88476 #t θ θdot θddot

2.50000 0.00890 0.57590 -1.15618 #t θ θdot θddot

2.51000 0.01454 0.56434 -1.41852 #t θ θdot θddot

2.52000 0.02004 0.55016 -1.67060 #t θ θdot θddot

2.53000 0.02537 0.53345 -1.91130 #t θ θdot θddot

2.54000 0.03052 0.51434 -2.13960 #t θ θdot θddot

2.55000 0.03545 0.49294 -2.35451 #t θ θdot θddot

2.56000 0.04014 0.46940 -2.55515 #t θ θdot θddot

2.57000 0.04458 0.44385 -2.74072 #t θ θdot θddot

2.58000 0.04874 0.41644 -2.91051 #t θ θdot θddot

2.59000 0.05262 0.38733 -3.06387 #t θ θdot θddot

2.60000 0.05618 0.35670 -3.20027 #t θ θdot θddot

2.61000 0.05943 0.32469 -3.31926 #t θ θdot θddot

2.62000 0.06235 0.29150 -3.42049 #t θ θdot θddot

2.63000 0.06492 0.25730 -3.50368 #t θ θdot θddot

2.64000 0.06714 0.22226 -3.56866 #t θ θdot θddot

2.65000 0.06901 0.18657 -3.61536 #t θ θdot θddot

2.66000 0.07051 0.15042 -3.64376 #t θ θdot θddot

2.67000 0.07165 0.11398 -3.65398 #t θ θdot θddot

2.68000 0.07243 0.07744 -3.64619 #t θ θdot θddot

2.69000 0.07284 0.04098 -3.62066 #t θ θdot θddot

2.70000 0.07288 0.00477 -3.57774 #t θ θdot θddot

2.71000 0.07257 -0.03101 -3.51785 #t θ θdot θddot

2.72000 0.07191 -0.06618 -3.44150 #t θ θdot θddot

2.73000 0.07091 -0.10060 -3.34926 #t θ θdot θddot

2.74000 0.06956 -0.13409 -3.24179 #t θ θdot θddot

2.75000 0.06790 -0.16651 -3.11978 #t θ θdot θddot

2.76000 0.06592 -0.19771 -2.98403 #t θ θdot θddot

2.77000 0.06365 -0.22755 -2.83535 #t θ θdot θddot

2.78000 0.06109 -0.25590 -2.67463 #t θ θdot θddot

2.79000 0.05826 -0.28265 -2.50281 #t θ θdot θddot

2.80000 0.05518 -0.30768 -2.32085 #t θ θdot θddot

2.81000 0.05188 -0.33088 -2.12978 #t θ θdot θddot

2.82000 0.04835 -0.35218 -1.93063 #t θ θdot θddot

2.83000 0.04464 -0.37149 -1.72447 #t θ θdot θddot

2.84000 0.04075 -0.38873 -1.51242 #t θ θdot θddot

2.85000 0.03671 -0.40386 -1.29557 #t θ θdot θddot

2.86000 0.03255 -0.41681 -1.07505 #t θ θdot θddot

2.87000 0.02827 -0.42756 -0.85199 #t θ θdot θddot

2.88000 0.02391 -0.43608 -0.62752 #t θ θdot θddot

2.89000 0.01949 -0.44236 -0.40275 #t θ θdot θddot

2.90000 0.01502 -0.44639 -0.17879 #t θ θdot θddot

2.91000 0.01054 -0.44817 0.04325 #t θ θdot θddot

2.92000 0.00606 -0.44774 0.26232 #t θ θdot θddot

2.93000 0.00161 -0.44512 0.47737 #t θ θdot θddot

2.94000 -0.00279 -0.44034 0.68739 #t θ θdot θddot

2.95000 -0.00713 -0.43347 0.89141 #t θ θdot θddot

2.96000 -0.01137 -0.42456 1.08851 #t θ θdot θddot

2.97000 -0.01551 -0.41367 1.27779 #t θ θdot θddot

2.98000 -0.01952 -0.40089 1.45842 #t θ θdot θddot

2.99000 -0.02338 -0.38631 1.62963 #t θ θdot θddot

3.00000 -0.02708 -0.37001 1.79070 #t θ θdot θddot

3.01000 -0.03060 -0.35211 1.94095 #t θ θdot θddot

3.02000 -0.03393 -0.33270 2.07979 #t θ θdot θddot

3.03000 -0.03705 -0.31190 2.20668 #t θ θdot θddot

3.04000 -0.03995 -0.28983 2.32116 #t θ θdot θddot

3.05000 -0.04261 -0.26662 2.42281 #t θ θdot θddot

3.06000 -0.04504 -0.24239 2.51130 #t θ θdot θddot

3.07000 -0.04721 -0.21728 2.58637 #t θ θdot θddot

3.08000 -0.04912 -0.19141 2.64782 #t θ θdot θddot

3.09000 -0.05077 -0.16494 2.69552 #t θ θdot θddot

3.10000 -0.05215 -0.13798 2.72942 #t θ θdot θddot

3.11000 -0.05326 -0.11069 2.74952 #t θ θdot θddot

3.12000 -0.05409 -0.08319 2.75590 #t θ θdot θddot

3.13000 -0.05465 -0.05563 2.74870 #t θ θdot θddot

3.14000 -0.05493 -0.02815 2.72812 #t θ θdot θddot

3.15000 -0.05494 -0.00086 2.69444 #t θ θdot θddot

3.16000 -0.05468 0.02608 2.64799 #t θ θdot θddot

3.17000 -0.05415 0.05256 2.58915 #t θ θdot θddot

3.18000 -0.05337 0.07845 2.51836 #t θ θdot θddot

3.19000 -0.05233 0.10363 2.43612 #t θ θdot θddot

3.20000 -0.05105 0.12800 2.34297 #t θ θdot θddot

3.21000 -0.04954 0.15143 2.23950 #t θ θdot θddot

3.22000 -0.04780 0.17382 2.12635 #t θ θdot θddot

3.23000 -0.04585 0.19508 2.00419 #t θ θdot θddot

3.24000 -0.04370 0.21513 1.87372 #t θ θdot θddot

3.25000 -0.04136 0.23386 1.73569 #t θ θdot θddot

3.26000 -0.03885 0.25122 1.59087 #t θ θdot θddot

3.27000 -0.03617 0.26713 1.44005 #t θ θdot θddot

3.28000 -0.03336 0.28153 1.28405 #t θ θdot θddot

3.29000 -0.03042 0.29437 1.12368 #t θ θdot θddot

3.30000 -0.02736 0.30561 0.95980 #t θ θdot θddot

3.31000 -0.02421 0.31520 0.79324 #t θ θdot θddot

3.32000 -0.02098 0.32314 0.62487 #t θ θdot θddot

3.33000 -0.01768 0.32939 0.45553 #t θ θdot θddot

3.34000 -0.01434 0.33394 0.28605 #t θ θdot θddot

3.35000 -0.01097 0.33680 0.11729 #t θ θdot θddot

3.36000 -0.00759 0.33797 -0.04994 #t θ θdot θddot

3.37000 -0.00422 0.33747 -0.21485 #t θ θdot θddot

3.38000 -0.00087 0.33533 -0.37664 #t θ θdot θddot

3.39000 0.00245 0.33156 -0.53456 #t θ θdot θddot

3.40000 0.00571 0.32621 -0.68789 #t θ θdot θddot

3.41000 0.00890 0.31934 -0.83592 #t θ θdot θddot

3.42000 0.01201 0.31098 -0.97799 #t θ θdot θddot

3.43000 0.01503 0.30120 -1.11349 #t θ θdot θddot

3.44000 0.01793 0.29006 -1.24183 #t θ θdot θddot

3.45000 0.02070 0.27764 -1.36247 #t θ θdot θddot

3.46000 0.02334 0.26402 -1.47490 #t θ θdot θddot

3.47000 0.02584 0.24927 -1.57870 #t θ θdot θddot

3.48000 0.02817 0.23348 -1.67345 #t θ θdot θddot

3.49000 0.03034 0.21675 -1.75880 #t θ θdot θddot

3.50000 0.03233 0.19916 -1.83445 #t θ θdot θddot

3.51000 0.03414 0.18082 -1.90016 #t θ θdot θddot

3.52000 0.03576 0.16181 -1.95573 #t θ θdot θddot

3.53000 0.03718 0.14226 -2.00101 #t θ θdot θddot

3.54000 0.03840 0.12225 -2.03592 #t θ θdot θddot

3.55000 0.03942 0.10189 -2.06041 #t θ θdot θddot

3.56000 0.04023 0.08128 -2.07449 #t θ θdot θddot

3.57000 0.04084 0.06054 -2.07823 #t θ θdot θddot

3.58000 0.04124 0.03976 -2.07174 #t θ θdot θddot

3.59000 0.04143 0.01904 -2.05517 #t θ θdot θddot

3.60000 0.04141 -0.00151 -2.02874 #t θ θdot θddot

3.61000 0.04119 -0.02180 -1.99270 #t θ θdot θddot

3.62000 0.04078 -0.04173 -1.94734 #t θ θdot θddot

3.63000 0.04016 -0.06120 -1.89300 #t θ θdot θddot

3.64000 0.03936 -0.08013 -1.83007 #t θ θdot θddot

3.65000 0.03838 -0.09843 -1.75895 #t θ θdot θddot

3.66000 0.03722 -0.11602 -1.68009 #t θ θdot θddot

3.67000 0.03589 -0.13282 -1.59398 #t θ θdot θddot

3.68000 0.03440 -0.14876 -1.50114 #t θ θdot θddot

3.69000 0.03276 -0.16377 -1.40209 #t θ θdot θddot

3.70000 0.03099 -0.17779 -1.29740 #t θ θdot θddot

3.71000 0.02908 -0.19077 -1.18765 #t θ θdot θddot

3.72000 0.02705 -0.20264 -1.07345 #t θ θdot θddot

3.73000 0.02492 -0.21338 -0.95540 #t θ θdot θddot

3.74000 0.02269 -0.22293 -0.83414 #t θ θdot θddot

3.75000 0.02038 -0.23127 -0.71030 #t θ θdot θddot

3.76000 0.01799 -0.23838 -0.58452 #t θ θdot θddot

3.77000 0.01555 -0.24422 -0.45744 #t θ θdot θddot

3.78000 0.01306 -0.24880 -0.32970 #t θ θdot θddot

3.79000 0.01054 -0.25209 -0.20193 #t θ θdot θddot

3.80000 0.00800 -0.25411 -0.07477 #t θ θdot θddot

3.81000 0.00545 -0.25486 0.05117 #t θ θdot θddot

3.82000 0.00291 -0.25435 0.17529 #t θ θdot θddot

3.83000 0.00038 -0.25260 0.29699 #t θ θdot θddot

3.84000 -0.00211 -0.24963 0.41572 #t θ θdot θddot

3.85000 -0.00457 -0.24547 0.53093 #t θ θdot θddot

3.86000 -0.00697 -0.24016 0.64209 #t θ θdot θddot

3.87000 -0.00931 -0.23374 0.74871 #t θ θdot θddot

3.88000 -0.01157 -0.22625 0.85032 #t θ θdot θddot

3.89000 -0.01375 -0.21775 0.94649 #t θ θdot θddot

3.90000 -0.01583 -0.20828 1.03681 #t θ θdot θddot

3.91000 -0.01781 -0.19792 1.12091 #t θ θdot θddot

3.92000 -0.01968 -0.18671 1.19846 #t θ θdot θddot

3.93000 -0.02142 -0.17472 1.26917 #t θ θdot θddot

3.94000 -0.02304 -0.16203 1.33276 #t θ θdot θddot

3.95000 -0.02453 -0.14870 1.38902 #t θ θdot θddot

3.96000 -0.02588 -0.13481 1.43776 #t θ θdot θddot

3.97000 -0.02708 -0.12044 1.47884 #t θ θdot θddot

3.98000 -0.02814 -0.10565 1.51215 #t θ θdot θddot

3.99000 -0.02905 -0.09053 1.53764 #t θ θdot θddot

4.00000 -0.02980 -0.07515 1.55526 #t θ θdot θddot

4.01000 -0.03039 -0.05960 1.56504 #t θ θdot θddot

4.02000 -0.03083 -0.04395 1.56702 #t θ θdot θddot

4.03000 -0.03112 -0.02828 1.56130 #t θ θdot θddot

4.04000 -0.03124 -0.01266 1.54799 #t θ θdot θddot

4.05000 -0.03121 0.00282 1.52726 #t θ θdot θddot

4.06000 -0.03103 0.01809 1.49930 #t θ θdot θddot

4.07000 -0.03070 0.03308 1.46434 #t θ θdot θddot

4.08000 -0.03022 0.04773 1.42263 #t θ θdot θddot

4.09000 -0.02961 0.06195 1.37448 #t θ θdot θddot

4.10000 -0.02885 0.07570 1.32018 #t θ θdot θddot

4.11000 -0.02796 0.08890 1.26009 #t θ θdot θddot

4.12000 -0.02694 0.10150 1.19457 #t θ θdot θddot

4.13000 -0.02581 0.11345 1.12402 #t θ θdot θddot

4.14000 -0.02456 0.12469 1.04883 #t θ θdot θddot

4.15000 -0.02321 0.13517 0.96943 #t θ θdot θddot

4.16000 -0.02176 0.14487 0.88628 #t θ θdot θddot

4.17000 -0.02023 0.15373 0.79981 #t θ θdot θddot

4.18000 -0.01861 0.16173 0.71050 #t θ θdot θddot

4.19000 -0.01692 0.16883 0.61882 #t θ θdot θddot

4.20000 -0.01517 0.17502 0.52524 #t θ θdot θddot

4.21000 -0.01337 0.18027 0.43026 #t θ θdot θddot

4.22000 -0.01152 0.18458 0.33436 #t θ θdot θddot

4.23000 -0.00964 0.18792 0.23801 #t θ θdot θddot

4.24000 -0.00774 0.19030 0.14169 #t θ θdot θddot

4.25000 -0.00582 0.19172 0.04588 #t θ θdot θddot

4.26000 -0.00390 0.19218 -0.04895 #t θ θdot θddot

4.27000 -0.00198 0.19169 -0.14236 #t θ θdot θddot

4.28000 -0.00008 0.19026 -0.23391 #t θ θdot θddot

4.29000 0.00180 0.18792 -0.32316 #t θ θdot θddot

4.30000 0.00365 0.18469 -0.40971 #t θ θdot θddot

4.31000 0.00545 0.18060 -0.49317 #t θ θdot θddot

4.32000 0.00721 0.17566 -0.57317 #t θ θdot θddot

4.33000 0.00891 0.16993 -0.64935 #t θ θdot θddot

4.34000 0.01054 0.16344 -0.72140 #t θ θdot θddot

4.35000 0.01210 0.15623 -0.78900 #t θ θdot θddot

4.36000 0.01359 0.14834 -0.85189 #t θ θdot θddot

4.37000 0.01499 0.13982 -0.90982 #t θ θdot θddot

4.38000 0.01629 0.13072 -0.96256 #t θ θdot θddot

4.39000 0.01750 0.12109 -1.00991 #t θ θdot θddot

4.40000 0.01861 0.11099 -1.05172 #t θ θdot θddot

4.41000 0.01962 0.10048 -1.08785 #t θ θdot θddot

4.42000 0.02052 0.08960 -1.11819 #t θ θdot θddot

4.43000 0.02130 0.07842 -1.14267 #t θ θdot θddot

4.44000 0.02197 0.06699 -1.16123 #t θ θdot θddot

4.45000 0.02252 0.05538 -1.17387 #t θ θdot θddot

4.46000 0.02296 0.04364 -1.18060 #t θ θdot θddot

4.47000 0.02328 0.03183 -1.18145 #t θ θdot θddot

4.48000 0.02348 0.02002 -1.17650 #t θ θdot θddot

4.49000 0.02356 0.00825 -1.16584 #t θ θdot θddot

4.50000 0.02353 -0.00341 -1.14960 #t θ θdot θddot

4.51000 0.02338 -0.01490 -1.12792 #t θ θdot θddot

4.52000 0.02312 -0.02618 -1.10098 #t θ θdot θddot

4.53000 0.02274 -0.03719 -1.06898 #t θ θdot θddot

4.54000 0.02226 -0.04788 -1.03214 #t θ θdot θddot

4.55000 0.02168 -0.05820 -0.99070 #t θ θdot θddot

4.56000 0.02100 -0.06811 -0.94491 #t θ θdot θddot

4.57000 0.02023 -0.07756 -0.89507 #t θ θdot θddot

4.58000 0.01936 -0.08651 -0.84146 #t θ θdot θddot

4.59000 0.01841 -0.09492 -0.78439 #t θ θdot θddot

4.60000 0.01738 -0.10277 -0.72418 #t θ θdot θddot

4.61000 0.01628 -0.11001 -0.66118 #t θ θdot θddot

4.62000 0.01512 -0.11662 -0.59572 #t θ θdot θddot

4.63000 0.01389 -0.12258 -0.52815 #t θ θdot θddot

4.64000 0.01261 -0.12786 -0.45884 #t θ θdot θddot

4.65000 0.01129 -0.13245 -0.38814 #t θ θdot θddot

4.66000 0.00993 -0.13633 -0.31643 #t θ θdot θddot

4.67000 0.00853 -0.13949 -0.24405 #t θ θdot θddot

4.68000 0.00711 -0.14193 -0.17139 #t θ θdot θddot

4.69000 0.00567 -0.14365 -0.09879 #t θ θdot θddot

4.70000 0.00423 -0.14464 -0.02661 #t θ θdot θddot

4.71000 0.00278 -0.14490 0.04480 #t θ θdot θddot

4.72000 0.00133 -0.14445 0.11509 #t θ θdot θddot

4.73000 -0.00010 -0.14330 0.18395 #t θ θdot θddot

4.74000 -0.00151 -0.14146 0.25103 #t θ θdot θddot

4.75000 -0.00290 -0.13895 0.31605 #t θ θdot θddot

4.76000 -0.00426 -0.13579 0.37871 #t θ θdot θddot

4.77000 -0.00558 -0.13201 0.43872 #t θ θdot θddot

4.78000 -0.00686 -0.12762 0.49583 #t θ θdot θddot

4.79000 -0.00808 -0.12266 0.54980 #t θ θdot θddot

4.80000 -0.00925 -0.11716 0.60039 #t θ θdot θddot

4.81000 -0.01037 -0.11116 0.64741 #t θ θdot θddot

4.82000 -0.01141 -0.10468 0.69066 #t θ θdot θddot

4.83000 -0.01239 -0.09778 0.72998 #t θ θdot θddot

4.84000 -0.01330 -0.09048 0.76523 #t θ θdot θddot

4.85000 -0.01412 -0.08283 0.79629 #t θ θdot θddot

4.86000 -0.01487 -0.07486 0.82305 #t θ θdot θddot

4.87000 -0.01554 -0.06663 0.84544 #t θ θdot θddot

4.88000 -0.01612 -0.05818 0.86341 #t θ θdot θddot

4.89000 -0.01662 -0.04954 0.87691 #t θ θdot θddot

4.90000 -0.01702 -0.04077 0.88595 #t θ θdot θddot

4.91000 -0.01734 -0.03191 0.89053 #t θ θdot θddot

4.92000 -0.01757 -0.02301 0.89068 #t θ θdot θddot

4.93000 -0.01771 -0.01410 0.88646 #t θ θdot θddot

4.94000 -0.01777 -0.00524 0.87795 #t θ θdot θddot

4.95000 -0.01773 0.00354 0.86524 #t θ θdot θddot

4.96000 -0.01761 0.01219 0.84844 #t θ θdot θddot

4.97000 -0.01740 0.02068 0.82770 #t θ θdot θddot

4.98000 -0.01711 0.02896 0.80315 #t θ θdot θddot

4.99000 -0.01674 0.03699 0.77497 #t θ θdot θddot

Answer 1

1. The preferred way would be to remove the empty lines created by your cpp output.

2. However, if you cannot or don't want to change your data, a gnuplot-only solution in short:

Script:

### remove empty lines via gnuplot
reset session

FILE = 'data/pendulum.md'

set table $Data
    set datafile separator "\n"         # read lines as a whole
    plot FILE u (strcol(1)) w table
    set datafile separator whitespace   # restore separator
unset table

plot for [i=2:4] $Data u 1:i w linesp title "θ(t) " . (i-2)
### end of script

Result: (depending on the size of the graph the lines are hardly visible)