How to save every iteration and answer for a numerical Solve function in a for loop

Hi everyone,

I have the following code

syms x g

for g=1.3099*10^15:0.05*10^15:2.6*10^15

      f=(((1.1096*10^17-(5.201*10^16)*(6.667*(x - 255)/x)^(1/3))/(g)) + 255-x);

      soln=solve(f,x)

end

I would like to save every value of g with its corresponding solution of x so that I can plot them,

Anyone got any ideas or changes I can make to achieve this?

Cheers,

Lindsey

Answer 1

[mashtine]

Hi Lindsey,

You can preallocate g outside of your loop and then within your loop you can assign each row and col the corresponding g value and solution:

syms x g

g=1.3099*10^15:0.05*10^15:2.6*10^15;

for i = 1:length(g)   % Assigns i for each value within in g
      f=(((1.1096*10^17-(5.201*10^16)*(6.667*(x - 255)/x)^(1/3))/(g(1,i))) + 255-x); % Will work on each g value and provide and f value
      soln=solve(f,x);
      finalsoln(1,i) = g;
      finalsoln(2,i) = soln;
end

This code will of course be different if you want your finalsoln matrix to be a 1xi or a ix1 matrix. However I am not too sure about using sym and the resultant x and the code as it stands raise a dimension mismatch but may be on my end.

Hope it makes sense

[lindsey Cameron]

Hi Masao,

THank you for your answer,

I get the following error,

Subscripted assignment dimension mismatch.

Would it be easier to just right the values to a text file? if so, how do I do that?

Cheers,

Lindsey

[lindsey Cameron]

I guess my goal at the end is to plot the change in x due to a change in g, do I even need to store it for that?

[mashtine]

Hi Lindsey,

As I am not familiar with the syms function (symbiotic relationship?) I am not sure how x is influenced. Your subscript dimension mismatch lies with this.

For instance, when this is run by itself:

syms x g
g=1.3099*10^15:0.05*10^15:2.6*10^15;

f=(((1.1096*10^17-(5.201*10^16)*(6.667*(x - 255)/x)^(1/3))/(g(1,i))) + 255-x);

g,x and f are produced but are empty sym variables and this is what caused the dimension mismatch. Did you define x before?