Solving parametric equations, fplot returning error " Input must be a function handle or symbolic function"

Hey there, trying to knock away at math problems on my own using MATLAB (since my college kinda just throws us in head first), and I am running into an issue. I have to convert a parametric equation to cartesian form, something easy enough on paper, but I am still having trouble with MATLAB and its syntax.

Here is my code:

syms t
syms x
syms y
eq = y == cos(t)
sol_t = solve(eq,t)
eq = y  == 3 + sin(t)
eq = subs(eq,t,sol_t)
axis equal
f(x) = eq(1)
fplot(f(x),[0,pi])

I think the problem is that at the end f(x) ends up becoming "f(x) = y == ..." but I don't know how to remove the y == part.

[Dimitris Kalogiros]

Which is the exact wording of your problem ?

[Walter Roberson]

Easy: change

eq = y  == 3 + sin(t)

to

eq = 3 + sin(t)

Answer 1

[Stephan]

Hi,

problably you look for this:

syms y
eq1 = y == cos(t)
sol_t = isolate(eq1,t)
eq2 = y == 3 + sin(t)
eq2 = y == subs(rhs(eq2),t,rhs(sol_t))
axis equal
fplot(rhs(eq2),[-pi,pi])

gives:

eq1 =

y == cos(t)

sol_t =

t == acos(y)

eq2 =

y == sin(t) + 3

eq2 =

y == (1 - y^2)^(1/2) + 3

Note that:

>> sin(acos(y)) + 3

ans =

(1 - y^2)^(1/2) + 3

plotted:

Best regards

Stephan