Question

I’m trying to use a LaTex string to insert a fraction for the y-axis label, and I get a number (in standard font and ylabel position) as well as what I expected (the fraction I’m trying to insert). This has changed for me when I’ve edited the code, but stopped once I tried investigating this (it’s 353.191 as I type, in case it helps). The number is not there if I don’t try to add a label to the y-axis, or add a label without LaTex. There is no error message.

Code in question:

ylabel(text('Interpreter','LaTex',...
    'string','$\frac{\tau_b(t)}{\phi \bar{U}}$',...
    'FontSize',20,'position',[-1.25,0.2]));

Full Program (above code is just before program finishes):

% --- MM3CAI Coursework 1 ---

clear all; clf('reset'); clc;

fig_num=0;

disp('Started program');
disp(' ');

% --- Task 1. About the water-brake only ---

disp('Started task 1');
disp(' ');

w_t=0.003;          % Volume of water in the brake at time t        [m^3]
thet_t=250;         % Angular velocity of brake at time t           [rads^-1]

percent=0.1;        % Percent added to values for small change      [%]
fraction=percent/100;

del_w=w_t*fraction;
del_t=thet_t*fraction;

w_del=w_t+del_w;
thet_del=thet_t+del_t;

clear percent fraction;

% --- Q1 ---

disp('Started question 1');
disp(' ');

tau  =150*w_t  *thet_t;
tau_w=150*w_del*thet_t;
tau_t=150*w_t  *thet_del;

tau_mat=[tau;...
     tau_w;...
     tau_t];

A=[w_t   thet_t   1;...
w_del thet_t   1;...
w_t   thet_del 1];

variables_mat=A\tau_mat;

phi=variables_mat(1,1);
psi=variables_mat(2,1);
eta=variables_mat(3,1);

disp(['Phi = ', num2str(phi)]);
disp(['Psi = ', num2str(psi)]);
disp(['Eta = ', num2str(eta)]);
disp(' ');

disp('Finished question 1');
disp('----------');

% --- Q2 ---

disp('Started question 2');
disp(' ');

beta=-eta/phi;

disp(['Beta = ', num2str(beta)]);
disp(' ');

disp('Finished question 2');
disp('----------');

% --- Q4 ---

disp('Started question 4');
disp(' ');

G=@(omega) phi./(1+(5i.*omega));

frequency=logspace(-3,3,700)';

G_mat=G(frequency);

phase_mat_rad=angle(G_mat);
phase_mat_deg=phase_mat_rad.*(180/pi);

magnitude_mat=abs(G_mat);
gain_mat=20.*log10(magnitude_mat);

fig_num=fig_num+1;
figure(fig_num);
subplot(2,1,1);
semilogx(frequency,gain_mat);
title('Bode Plot');
xlabel('Frequency [rads^-^1]');
ylabel('Gain [dBs]');
subplot(2,1,2);
semilogx(frequency,phase_mat_deg);
xlabel('Frequency [rads^-^1]');
ylabel('Phase Angle [degrees]');

disp('Finished question 4');
disp('----------');

% --- Q5 ---

disp('Started question 5');
disp(' ');

U_bar=1;
step=@(t) (phi*U_bar)*(1-exp(-t/5));

time=(0:0.01:8);

step_mat=step(time);
normalised=step_mat./(phi*U_bar);

fig_num=fig_num+1;
figure(fig_num);
plot(time,normalised);
title('Step Response');
xlabel('Time [s]');
ylabel(text('Interpreter','LaTex',...
        'string','$\frac{\tau_b(t)}{\phi \bar{U}}$',...
        'FontSize',20,'position',[-1.25,0.2]));

disp('Finished question 5');
disp('----------');

I’m really confused by this, which makes it harder to find anything. All I could find was basic MatLab help about using LaTex (which is how I muddled the string together) and people having issues where text() wasn’t working and generating an error – nothing where the expected output was generated and something else appeared.

Answer 1

TEXT function returns the handle to text object, which is actually a number. This is the number you get as y-label. You only need to pass the string as the first argument to YLABEL and specify the Interpreter (and FontSize) property:

ylabel('$\frac{\tau_b(t)}{\phi \bar{U}}$','Interpreter','LaTex','FontSize',20);

Position is determined automatically by ylabel.

In your ylabel statement the text object is actually created (this is why you don’t get an error), but the position chosen in such a way that the text is outside of the visible area. -1.25 means the text is located 1.25 of the axes size to the left.

You can also use text object along as axes label, but you will have to adjust the text position with axes size change.

text('Interpreter','LaTex',...
    'string','$\frac{\tau_b(t)}{\phi \bar{U}}$',...
    'FontSize',20,'position',[-0.1,0.5]);

Notice, Position property is not x and y, but axes fractions.