How to define the value of "t" from function f(t)

Hello,

I have a function

   f(t)=exp(-0.01*t.^2).*cos(2.*t)

where 't' is a function handle (f=@t)

I need to define 't' when f(t)=0.4.

How do I do this?

Sergey

Answer 1

[Walter Roberson]

It sounds to me like you might be attempting to solve exp(-0.01*t.^2).*cos(2.*t) to find the t where the expression becomes 0.4 . If so then there are an infinite number of solutions. You can find one of them by using

syms f(t)
f(t) = exp(-0.01*t.^2).*cos(2.*t);
vpasolve(f(t)=0.4)

[Sergey Dukman]

Hello, Yes, you are right. I need to find t when f(t)=0.4. Thank you for help!

Sergey

[Steven Lord]

Or if you don't have Symbolic Math Toolbox, you could use FZERO from MATLAB. Rewrite your expression so it's in the form g(t) = 0:

 f = @(t) exp(-0.01*t.^2).*cos(2.*t);
 g = @(t) f(t)-0.4; % Transforming f(t) = 0.4 -> f(t)-0.4 = 0

Then call FZERO to find a zero of g(t). Change the initial guess to locate additional zeros.

 fzero(g, 0)