Trying to store values from a while into a 1D array and plot a graph with the values.

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Maximillian Springer 2017-1-13

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回答： Jyotish Robin 2017-1-16

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The following is my program so far:

% MATLAB M-file to solve a single equation using the Rearrangement method.

% The function is f(x)= cos^3(x) - x = 0 and the rearranged function % is g(x) = cos^-1(x^1/3).

clc % clear command window clear % clear workspace

k = 0; % Set the iteration number x = 0; % Set the starting value

diff = 1; % Set the difference between successive x values % to an arbitrary value to start the iteration

fprintf(' k xk\n') fprintf('%5i%10.4f\n', k, x) % output the starting value

while diff > 0.6e-4 % Continue until convergence is achieved to 5 decimal places

   xlast = x; 
   x = 1/(cos(xlast^1/3));  %  defines x(k+1) = g(x(k))
   diff = abs(x - xlast);  % Calculate the difference between two successive iterations
   k = k + 1;   % Add 1 to the iteration number
   fprintf('%5i%10.4f\n', k, x)  % Output the intermediate solutions to 6 decimal places

end

I am trying to modify this program such that it plots a graph of the iteration numbers against the x values, once covergence is acheived, by storing the x values in a 1D array.

Thanks in advance, fairly new to matlab.

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Answer 1

Jyotish Robin 2017-1-16

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Hi Maximillian,

Happy to hear that you are using MATLAB .

I understand that you would like to plot a graph of x-values against the iteration number. You could probably store the x-values in each iteration to an array (say, values) by including the following line in your code after the line which corresponds to incrementing k value :

>>values(k)=x;

Now, you can use the "stem" function to plot the "values" against the iteration number as follows:

>>stem(values);

Since you are new to MATLAB, I would recommend you to take a look at the documentation to know about the "stem" function:

https://www.mathworks.com/help/matlab/ref/stem.html