Fsolve Intemidiate equations result

have a problem with MatLAB fsolve. How can I get the intermediate calculations for a given function? not only for the desired variable, but also for the equations included in the system for fsolve

fsolve code

function solve_syst ()

a_init = -2;

b = 5;

c = 6;

d = 8;

syst_eq = @(a) syst_3 (a, b, c, d);

%options = optimoptions('fsolve','Display','none', 'outputFcn')

[a_vih, fval] = fsolve (syst_eq, a_init);

end

first eq

function x1 = syst_1 (a, b) %first eq

x1 = a * 6 + 2 * b;

end

second eq

function x2 = syst_2 (c, d)%second eq

x2 = c * 4 - d * 2;

end

system for fsolve

function [prov, x1, x2] = syst_3 (a, b, c, d) %system for fsolve

x1 = syst_1 (a, b)

x2 = syst_2 (c, d)

prov = x1 - x2;

end

fsolve calculates intermediate values ​​x1 and x2 (visible in the command window), but I cannot get these values ​​separately to use in further calculations

Answer 1

[Alan Weiss]

You could use persistent variables along with assignin to write the variaible value to a workspace variable. Something like this:

function [prov, x1, x2] = syst_3 (a, b, c, d) %system for fsolve
persistent x1x2hist
x1 = syst_1 (a, b)
x2 = syst_2 (c, d)
x1x2hist = [x1x2hist;x1,x2];
assignin('base','x1x2hist',x1x2hist);
prov = x1 - x2;
end

That said, I think that it is a mistake to use fsolve to solve a linear system of equations. Instead, you should use the backslash command. You might also benefit from using the problem-based approach.

Good luck,

Alan Weiss

MATLAB mathematical toolbox documentation

[Rofl One]

Thank you!

Answer 2

[Matt J]

After solving, you can simply use the objective function that you have already written to obtain these values:

[a_vih, fval] = fsolve (syst_eq, a_init);

[~, x1, x2] = syst_eq(a_vih)