iterate fsolve and save each iterated result

hi every body. im using fsolve to solve 3x3 non linear system. i have a parameter (velocity) that i want to encrease every time i solve the 3x3 system. my question is, how i iterate fsolve and how i save the results. i have this main file that call the fsolve

clc
clear all
basico; 

uo2=1;
yo2=0.1;
yo3=0.1;

x0 = [uo2; yo2; yo3];           % Make a starting guess at the solution
options=optimset('Display','iter');% Option to display output
[x,fval] = fsolve(@func,x0,options)  % Call solver

so every time i solve the system i get a vector x with 3 values solved by fsolve. i want to iterate FSOLVE and in each iteration increase a parameter inside FUNC file and save the results for plot it.

any idea? thanks for advance =)

Answer 1

[Walter Roberson]

options=optimset('Display','iter');% Option to display output

x0 = [uo2; yo2; yo3];           % Make a starting guess at the solution

maxiter = 1000;     %however many
x = zeros(1, maxiter);
fval = zeros(1, maxiter);

for ITER = 1 : maxiter    %however many
  newparam = revise_parameter(ITER, maxiter);   %a function to return the revised parameter
  [x(ITER), fval(ITER)] = fsolve(@(x) func(x, newparam), x0, options);
  x0 = x(ITER);
end

plot(x, fval);

This would involve adding the "parameter inside FUNC file" as an argument to func, and would involve creating a new function revise_parameter that accepts the current iteration number and maximum iteration limit and returns the value that you would otherwise have revised the "parameter inside FUNC file" to.

[MEXICO]

thanks for the answer!!!. i tried this:

clc

options=optimset('Display','iter');% Option to display output

ao=-5;

bo=-5;

k=100;

uamax=1;

uamin=10;

dua=(uamax-uamin)/k;

x0 = [ao; bo;]; % Make a starting guess at the solution

x = zeros(1, k);

fval = zeros(1, k);

for n = 1 : k %however many

ua=(n*dua)+uamin;   %a function to return the revised parameter

[x(n), fval(n)] = fsolve(@(x) myfun(x,ua), x0, options);
 x0 = x(n);

end

plot(x, fval);

but i get this error msg

??? In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in ==> main at 19 [x(n), fval(n)] = fsolve(@(x) myfun(x,ua), x0, options);

but the idea is clear, i want to change the value of "ua" each iteration and save each "x" results

=)

[Walter Roberson]

You have a logical problem: you want to plot fval against x, but you are solving for two x values. You should probably be plotting the two x and the fval against ua.

x = zeros(k, 2);   %note switch to columns
fval = zeros(k, 1);  %switched to column
ua = zeros(k, 1);

for n = 1 : k
  ua(n) = (n*dua) + uamin;
  [x(n,:), fval(n)] = fsolve(@(x) myfun(x,ua), x0, options);
  x0 = x(n,:);
end

plot(ua, [fval, x]);   %plot makes one line for each column of y

[MEXICO]

thanks for your answer, now im getting results!!!, i have a question with "x0 = x(n,:);" every iteration i will have new starting guesses?

[Walter Roberson]

The starting guess for iteration #n will be the output from iteration #(n-1)

[MEXICO]

i have this

for n = 2:k;

ua(1)=uamin; 
ua(n) =ua(n-1)+dua;

 [x((n-1),:)] = fsolve(@(x) func(x,ua(n-1)), x0, options)

x0 = x((n-1),:);

end