Error using feval Function to evaluate must be represented as a string scalar, character vector, or function_handle object.

f(t)=[-cos(t), -sin(t), 2*cos(t)^3 - 7*cos(t)*sin(t)^2]

feval(f(t),3.14)

I'd like to evaluate the vector value function above at 3.14, but I get the error message in the subject line. How do I fix this?

[William Gibson]

The error messages are listed below:

Error using feval

Function to evaluate must be represented as a string scalar, character vector, or function_handle object.

Error in untitled2 (line 2)

feval(f(t),3.14)

Answer 1

[Steven Lord]

Another approach, if you don't want to work symbolically as @Walter Roberson did, is to create an anonymous function. All I needed to do was move the equals sign and add an @ symbol.

f = @(t) [-cos(t), -sin(t), 2*cos(t)^3 - 7*cos(t)*sin(t)^2]

f = function_handle with value:
    @(t)[-cos(t),-sin(t),2*cos(t)^3-7*cos(t)*sin(t)^2]

feval(f,3.14)

ans = 1×3

1.0000 -0.0016 -2.0000

But with an anonymous function you don't even need feval.

y = f(3.14)

y = 1×3

1.0000 -0.0016 -2.0000

Given what you're doing the pi function may be of interest to you, as may the cospi and sinpi functions.

[William Gibson]

thanks!!!

Answer 2

[Walter Roberson]

syms t
f(t)=[-cos(t), -sin(t), 2*cos(t)^3 - 7*cos(t)*sin(t)^2]

f(t) = 

Then

output = feval(f,3.14)   %must "use" the output

output = 

or

f(3.14)     %do not need to "use" the output

ans = 

or

subs(f(t), t, 3.14)  %do not need to "use" the output

ans =