MATLAB: Wrong axis scale on plot when using sqrt

automatic;axisplotsqrtwrong

Hello guys,
I am trying to see these plot, but when i use the square root on Y axis, my plot doesnt show properly the data, he dont do change his axis automatic, only show the data when i dont use squase root, and i dont know why.
% Imported data 
  set(gcf, 'Visible','off'); % turns current figure "off" 
  set(0, 'DefaultFigureVisible','off'); % all subsequent figures "off" 
                kC1=[
                 0.000  -00.1169E-09
                 -0.100  -00.1367E-09
                 -0.200  -00.1348E-09
                 -0.300  -00.1390E-09
                 -0.400  -00.1436E-09
                 -0.500  -00.1504E-09
                 -0.600  -00.1595E-09
                 -0.700  -00.1708E-09
                 -0.800  -00.1872E-09
                 -0.900  -00.2085E-09
                 -1.000  -00.2355E-09
                 -1.100  -00.2686E-09
                 -1.200  -00.3095E-09
                 -1.300  -00.3533E-09
                 -1.400  -00.4076E-09
                 -1.500  -00.4702E-09
                 -1.600  -00.5477E-09
                 -1.700  -00.6392E-09
                 -1.800  -00.7473E-09
                 -1.900  -00.8695E-09
                 -2.000  -01.0096E-09
                 -2.100  -01.1606E-09
                 -2.200  -01.3258E-09
                 -2.300  -01.5029E-09
                 -2.400  -01.6870E-09
                 -2.500  -01.8784E-09
                 -2.600  -02.0757E-09
                 -2.700  -02.2754E-09
                 -2.800  -02.4786E-09
                 -2.900  -02.6829E-09
                 -3.000  -02.8866E-09
                 -3.100  -03.0918E-09
                 -3.200  -03.2991E-09
                 -3.300  -03.5086E-09
                 -3.400  -03.7128E-09
                 -3.500  -03.9205E-09
                 -3.600  -04.1254E-09
                 -3.700  -04.3283E-09
                 -3.800  -04.5317E-09
                 -3.900  -04.7324E-09
                 -4.000  -04.9373E-09
                 -4.100  -05.1375E-09
                 -4.200  -05.3333E-09
                 -4.300  -05.5360E-09
                 -4.400  -05.7326E-09
                 -4.500  -05.9295E-09
                 -4.600  -06.1273E-09
                 -4.700  -06.3270E-09
                 -4.800  -06.5270E-09
                 -4.900  -06.7258E-09
                 -5.000  -06.9226E-09
                ];
                 VC1=kC1(:,1);
                 IC1=kC1(:,2);
                 plot(VC1,IC1);
                 xlabel('Gate Voltage Vg (V)');
                 ylabel('Drain-Source Current (A)');
                title('422.21 OSC8 INV1 BIG');
                % Figure and plot 
                figure('units','normalized','outerposition', [0 0 1 1]); 
                plot(kC1(:,1),sqrt(kC1(:,2)),'LineWidth',1);
                set(gcf, 'Visible','on'); % turns current figure "on"
                set(0, 'DefaultFigureVisible','on'); % all subsequent figures "on"
                % Axis FTS norm for articles
                xlabel('$V_g (V)$','Interpreter','latex','fontsize', 20,'FontWeight','bold');
                ylabel('$\sqrt{ I_{DS} (A)}$','Interpreter','latex','fontsize', 20,'FontWeight','bold');
                axis('square');
                set(gcf, 'color','w');
                % Color the curves to black
                set(0, 'DefaultAxesColorOrder', [0 0 0] ,'DefaultAxesLineStyleOrder','-');
                set(gca, 'FontSize',20);
Anyone knows why?

Best Answer

The reason is that your ‘kCl’ data are all negative, so the square roots are all going to be pure imaginary.
See if:
plot(kC1(:,1),imag(sqrt(kC1(:,2))),'LineWidth',1);
produces the plot you want. Note that you will likely have to mention in your plot (or somewhere in your paper) that you are plotting the imaginary results of the square root operation on your ‘IC1’ variable (what ‘kCl(:,2)’ actually seems to be).
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