Using curve fitting with solve function

Using formula(curvefit) I can get the polynomial function of the curvefit to show in the command window.

I would like to use that polynomial equation togheter with a function handle, that comes from another function file, and pass them to a the solve function to solve for one of the two variables.

I_sc has variables x and y.

I_sc_max only has variable y (the same y as I_sc).

The second problem is that i want to use the solution (one of the solutions) from the solve function as a function handle.

Thanks for any help!

This code is my try at solving the problem but using the == sign doesn't work well with sfit.

Error:

Undefined function 'eq' for input arguments of type 'sfit'.

syms x y;

% Curve fit: poly23.
% formula(curvefit) shows the sfit uses variables x and y.
I_sc = curvefit;    % sfit

I_sc_max = I_sc_max_function(); % function handle from other file. Variable y.


eqn = I_sc == I_sc_max;    %<--- ERROR

S = solve( eqn, x );    % Gives two solutions
S1= S(1);               % Extracting one solution

% Want to use solution as function handle.

func =@(y) S1;

Answer 1

[Sai Bhargav Avula]

I_sc value is an object of the sfit. The solve function requires a polynomial expression. Using the attributes(coeffvalues,coeffnames) of sfit object the function handle for the polynomial can be obtained.

% Extract coefficient names 
names = coeffnames(I_sc); 
  
I_sc_expression = 0; 
% Looping to construct the polynomial expression.  
for i = 1:numel(names) 
    name = names{i}; 
    I_sc_expression =  I_sc_expression + I_sc.(name)* (x^str2double(name(2)) * y^str2double(name(3))); 
end 

eqn = I_sc_expression == I_sc_max;

S = solve( eqn, x );    % Gives two solutions
S1= S(1);               % Extracting one solution

func =@(y)subs(S1,y);