How to pass a variable with latex interpreter in the legend?

I am mentioning the relevant part of the code below. r_Fit is supposed to be a variable. How do I pass its value in the legend with a mathematical expression, $\tau = $ attached to it? Please help.

a_Fit = output_parameters(1);
r_Fit = output_parameters(2);
r_Fit_Str = num2str(r_Fit);
N_AS_Above3_Fit = a_Fit.*N_Days.^(-r_Fit);
figure(002);
plot(N_Days, N_AS_Above3, '+', 'LineWidth', 3, 'MarkerSize', 14, 'MarkerEdgeColor', 'r');
hold on;
plot(N_Days, N_AS_Above3_Fit, 'k', 'LineWidth', 3);
lgd = legend({'$M>3$', '$\tau = $ r_Fit'}, 'interpreter', 'latex');

Answer 1

[Walter Roberson]

lgd = legend(["$M>3$", "$\tau = $ " + r_Fit], 'interpreter', 'latex');

This will convert r_Fit according to internal (and seemingly inconsistent) rules about how many digits should be converted.

If you need more certainty in the formatting, use compose

[Vikash Pandey]

Thanks Walter. With the round command I could control the number of desired decimal places. It helped!

[Vikash Pandey]

One more question. I wish to add another variable in the second legend. I tried this, but it did not worked. It only prints the first legend and the first part of the second legend.

lgd = legend(["$M>3$", "$\tau = $ " + a_Fit   "$p = $ "   + r_Fit], 'interpreter', 'latex');

[Walter Roberson]

lgd = legend(["$M>3$", "$\tau = $ " + a_Fit + " $p = $ "   + r_Fit], 'interpreter', 'latex');

Answer 2

[Dyuman Joshi]

Use compose to generate the string, modify it and use it as an input to legend().

Note that added \ before \tau.

str = compose(['$\\tau = $ %f'], r_fit)
str = [{'$M>3$'} str];
legend(str, 'interpreter', 'latex');

Change the modifier according to the data-type and according to the number of digits you want to show.

[Vikash Pandey]

One more question. I wish to add another variable in the second legend. I tried this, but it did not worked. It only prints the first legend and the first part of the second legend.

a_Fit = round(output_parameters(1), 2);
r_Fit = round(output_parameters(2), 2);
N_AS_Above3_Fit = a_Fit.*N_Days.^(-r_Fit);
figure(002);
plot(N_Days, N_AS_Above3, '+', 'LineWidth', 3, 'MarkerSize', 14, 'MarkerEdgeColor', 'r');
hold on;
plot(N_Days, N_AS_Above3_Fit, 'k', 'LineWidth', 3);
lgd = legend(["$M>3$", "$\tau = $ " + a_Fit   "$p = $ "   + r_Fit], 'interpreter', 'latex');

[Dyuman Joshi]

There's a missing + sign -

%                                           v
lgd = legend(["$M>3$", "$\tau = $ " + a_Fit + " $p = $ "   + r_Fit], 'interpreter', 'latex');

[Vikash Pandey]

Thanks, Dyuman. it worked.

[Dyuman Joshi]

You're welcome!