In this example, we use the genetic algorithm (-g) and optimise for gain (1), F/B (2) and SWR (16), while aiming for an input resistance of 12.5 Ohms.

parrot /export/home/drkirkby/yagiuda-1.18/src % optimise -g 19 -Z12.5 example1 1000
Will optimise using a genetic algorithm
Optimising for maximum possible gain.
Optimising for maximum possible FB ratio.
Optimising for an input SWR as low as possible
G= 9.65dBi,FB= 12.30dB,SL= 0.00dB,SWR= 5.18,Z= 42.42-j 29.86,0.328
1 G= 9.35dBi,FB= 10.38dB,SL= 0.00dB,SWR= 3.04,Z= 12.44+j 14.57,0.387
5 G= 8.55dBi,FB=  9.36dB,SL= 0.00dB,SWR= 1.84,Z= 20.54-j  5.77,0.420
7 G= 9.29dBi,FB= 12.34dB,SL= 0.00dB,SWR= 2.32,Z= 28.40+j  3.72,0.427
8 G= 8.71dBi,FB= 11.49dB,SL= 0.00dB,SWR= 1.86,Z= 17.96-j  7.76,0.429
8 G= 9.67dBi,FB= 11.86dB,SL= 0.00dB,SWR= 2.17,Z= 25.51+j  5.55,0.454
8 G= 9.13dBi,FB= 12.17dB,SL= 0.00dB,SWR= 1.78,Z= 14.39-j  7.64,0.457
8 G= 9.30dBi,FB= 11.86dB,SL= 0.00dB,SWR= 1.44,Z= 17.81-j  1.39,0.495
9 G= 9.66dBi,FB= 10.69dB,SL= 0.00dB,SWR= 1.27,Z= 15.63+j  1.04,0.529
10 G= 9.63dBi,FB=  9.95dB,SL= 0.00dB,SWR= 1.21,Z= 15.07+j  0.12,0.533
11 G= 9.50dBi,FB= 11.42dB,SL= 0.00dB,SWR= 1.17,Z= 14.55+j  0.45,0.535
11 G=10.17dBi,FB= 11.06dB,SL= 0.00dB,SWR= 1.18,Z= 11.53+j  1.72,0.564
18 G=10.17dBi,FB= 11.08dB,SL= 0.00dB,SWR= 1.09,Z= 11.48+j  0.32,0.575
29 G=10.10dBi,FB= 11.33dB,SL= 0.00dB,SWR= 1.05,Z= 11.90-j  0.04,0.578
33 G=10.11dBi,FB= 11.45dB,SL= 0.00dB,SWR= 1.05,Z= 11.96+j  0.10,0.579
33 G=10.12dBi,FB= 11.57dB,SL= 0.00dB,SWR= 1.04,Z= 12.02+j  0.23,0.580
45 G=10.11dBi,FB= 11.58dB,SL= 0.00dB,SWR= 1.04,Z= 12.04+j  0.23,0.580
47 G=10.07dBi,FB= 11.59dB,SL= 0.00dB,SWR= 1.02,Z= 12.34+j  0.17,0.582
49 G=10.06dBi,FB= 11.58dB,SL= 0.00dB,SWR= 1.02,Z= 12.38+j  0.17,0.582
54 G=10.09dBi,FB= 11.70dB,SL= 0.00dB,SWR= 1.02,Z= 12.29+j  0.07,0.583
57 G=10.08dBi,FB= 11.70dB,SL= 0.00dB,SWR= 1.01,Z= 12.34+j  0.06,0.583
59 G=10.08dBi,FB= 11.69dB,SL= 0.00dB,SWR= 1.01,Z= 12.36+j  0.06,0.583
62 G=10.07dBi,FB= 11.69dB,SL= 0.00dB,SWR= 1.01,Z= 12.41+j  0.06,0.583
99 G=10.28dBi,FB= 12.49dB,SL= 0.00dB,SWR= 1.05,Z= 11.89+j  0.15,0.589
100 G=10.21dBi,FB= 12.75dB,SL= 0.00dB,SWR= 1.02,Z= 12.32-j  0.13,0.592
100 G=10.39dBi,FB= 13.66dB,SL= 0.00dB,SWR= 1.06,Z= 11.81-j  0.13,0.597
101 G=10.39dBi,FB= 13.72dB,SL= 0.00dB,SWR= 1.06,Z= 11.86-j  0.18,0.597
101 G=10.73dBi,FB= 11.03dB,SL= 0.00dB,SWR= 1.06,Z= 11.92+j  0.48,0.605
110 G=10.74dBi,FB= 11.09dB,SL= 0.00dB,SWR= 1.06,Z= 11.91+j  0.42,0.606
113 G=10.74dBi,FB= 11.01dB,SL= 0.00dB,SWR= 1.04,Z= 12.41+j  0.43,0.610
117 G=10.74dBi,FB= 10.87dB,SL= 0.00dB,SWR= 1.02,Z= 12.28+j  0.09,0.612
135 G=11.63dBi,FB= 18.12dB,SL= 0.00dB,SWR= 1.59,Z=  8.73-j  3.12,0.625
143 G=11.68dBi,FB= 19.26dB,SL= 0.00dB,SWR= 1.71,Z=  8.41-j  3.75,0.630
144 G=11.70dBi,FB= 19.72dB,SL= 0.00dB,SWR= 1.67,Z=  8.48-j  3.51,0.640
145 G=11.68dBi,FB= 16.78dB,SL= 0.00dB,SWR= 1.24,Z= 11.25+j  2.18,0.652
149 G=11.53dBi,FB= 17.96dB,SL= 0.00dB,SWR= 1.25,Z= 11.15+j  2.24,0.654
151 G=11.58dBi,FB= 18.48dB,SL= 0.00dB,SWR= 1.23,Z= 11.06+j  1.93,0.664
152 G=11.76dBi,FB= 18.76dB,SL= 0.00dB,SWR= 1.22,Z= 10.44+j  1.01,0.676
156 G=11.74dBi,FB= 19.23dB,SL= 0.00dB,SWR= 1.20,Z= 10.63+j  0.97,0.683
167 G=11.74dBi,FB= 19.23dB,SL= 0.00dB,SWR= 1.18,Z= 10.61+j  0.27,0.686
168 G=11.75dBi,FB= 19.82dB,SL= 0.00dB,SWR= 1.21,Z= 10.43+j  0.65,0.691
168 G=11.12dBi,FB= 24.86dB,SL= 0.00dB,SWR= 1.26,Z= 15.73+j  0.64,0.794
170 G=11.17dBi,FB= 34.19dB,SL= 0.00dB,SWR= 1.19,Z= 14.29-j  1.56,0.935
174 G=11.18dBi,FB= 37.25dB,SL= 0.00dB,SWR= 1.20,Z= 14.06-j  1.81,0.935
179 G=11.19dBi,FB= 32.58dB,SL= 0.00dB,SWR= 1.19,Z= 14.12-j  1.59,0.937
186 G=11.17dBi,FB= 35.02dB,SL= 0.00dB,SWR= 1.17,Z= 14.22+j  1.12,0.938
191 G=11.32dBi,FB= 26.96dB,SL= 0.00dB,SWR= 1.13,Z= 14.09-j  0.12,0.947
195 G=11.33dBi,FB= 28.27dB,SL= 0.00dB,SWR= 1.11,Z= 13.87-j  0.38,0.952
205 G=11.32dBi,FB= 29.37dB,SL= 0.00dB,SWR= 1.11,Z= 13.31-j  1.09,0.952
207 G=11.39dBi,FB= 27.16dB,SL= 0.00dB,SWR= 1.11,Z= 13.51-j  0.92,0.956
501 G=11.69dBi,FB= 29.56dB,SL= 0.00dB,SWR= 1.13,Z= 12.06+j  1.44,0.967
506 G=11.75dBi,FB= 27.15dB,SL= 0.00dB,SWR= 1.14,Z= 11.51+j  1.16,0.970
508 G=11.71dBi,FB= 28.73dB,SL= 0.00dB,SWR= 1.12,Z= 11.76+j  1.18,0.970
520 G=11.61dBi,FB= 29.20dB,SL= 0.00dB,SWR= 1.07,Z= 11.89+j  0.62,0.971
536 G=11.64dBi,FB= 31.64dB,SL= 0.00dB,SWR= 1.08,Z= 11.64+j  0.41,0.971
548 G=11.63dBi,FB= 31.09dB,SL= 0.00dB,SWR= 1.08,Z= 11.70+j  0.46,0.971
572 G=11.50dBi,FB= 31.55dB,SL= 0.00dB,SWR= 1.01,Z= 12.60-j  0.14,0.974
579 G=11.56dBi,FB= 43.43dB,SL= 0.00dB,SWR= 1.01,Z= 12.44-j  0.03,0.978
584 G=11.64dBi,FB= 29.79dB,SL= 0.00dB,SWR= 1.02,Z= 12.39+j  0.17,0.980
613 G=11.64dBi,FB= 30.11dB,SL= 0.00dB,SWR= 1.02,Z= 12.32+j  0.12,0.981
The best design is in a file "example1.bes". You should check it thoroughly
and if its better than example1, copy example1.bes to example1
parrot /export/home/drkirkby/yagiuda-1.18/src %

The last column of output shows a number that increases all the time. This is the goodness of the antenna. The GA uses this value and considers the antenna better if this number is bigger. The goodness is calculated from the a weighted average of the parameters you optimise for - in this case gain, FB and VSWR. We can set our own weighting factor if we wish. See #4.