fzero of function 3 variables

function dydt = eqdiff(t,y,lambda)
 dydt=-lambda*y
lambda=1

I write

fzero( @eqdiff(t,y,lambda),2)

matlab give me errore message

how i can solve the zero of a function

[Torsten]

Could you clearly state the problem you are trying to solve ?

[raffaele orlando]

i want to use fzero for the function dydt . can i use fzero for function as dydt(3 variables)?if yes how?

[Torsten]

So in the simple case you stated, you want to know for which value of y the expression -lambda*y becomes zero ?

[raffaele orlando]

yes

Answer 1

[Ameer Hamza]

To solve the equation with multiple input variables, use fsolve. Also, the input can be multi-dimensional, but the variable needs to be the same. For example

fsolve(@(x) eqdiff(x(1),x(2),x(3)), zeros(1,3))

function dydt = eqdiff(t,y,lambda)
dydt=-lambda*y;
lambda=1;
end

Answer 2

[Walter Roberson]

fzero() is designed for single functions of one variables that return scalar values.

fsolve() from the Optimization toolbox can handle multiple variables (and multiple functions.)

Sometimes what you can get away with is

fminunc( @(tyl) eqdiff(tyl(1), tyl(2), tyl(3)).^2, initial_values)

However,

function dydt = eqdiff(t,y,lambda)
 dydt=-lambda*y
lambda=1

That last line confuses me. You have lambda on input but you assign 1 to it inside the function? What are you expecting that would do for you?

I suspect that you are using the wrong approach to what you are doing. I suspect that you are trying to solve a boundary value problem; see https://www.mathworks.com/help/matlab/boundary-value-problems.html for those.

Your function has trivial solutions: just let y or lambda be 0.