two functions with descriptions in one graph

for this code:

% approximating f
plot(X_in.', U.');
xlabel('x');
ylabel('approximate f(x)');

legend_strs = compose('Approximate f with h=%.2d', h);
legend(legend_strs);

I get the followin graph (for two different axis steps h = [0.2, 0.025]):

What I want is to add another function to the same graph (true function f) and to add a description of the line in the above right section saying "true function f".

say that f = cos(2x)

how can I do this?

Thank you.

[VBBV]

What is the equation of true function f ?

[danielle sisserman]

f = cos(2x)

Answer 1

[Walter Roberson]

f = @(x) cos(2*x);
plot(X_in.', U.', X_in.', f(X_in.'));
xlabel('x');
ylabel('approximate f(x)');
legend_strs = [compose('Approximate f with h=%.2d', h), "true function f"];
legend(legend_strs);