Why isn't my y value changing?

Question

Xavier Bardwell 2021-11-23

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https://ww2.mathworks.cn/matlabcentral/answers/1594129-why-isn-t-my-y-value-changing

回答： Image Analyst 2021-11-23

I have a while loop where i iterate through polyval calculations an unkown amount of times based on the r^2 value. My loop currently runs infinitely because my y values are not changing as the order changes. WHy isnt my y value changing and how can i fix it?

while rSQ < .95
         y = polyval(polyfit(x,y,currOrder), x)
         
         rSQTop = (yOG - y).^2
         rSQBot = (yOG - yAVG).^2
         rSQ = 1 - (sum(rSQTop) / sum(rSQBot))
         
         if rSQ > .95
             plot(x,y,'b-')
         else
             plot(x,y,'r--');
             currOrder = currOrder + 1;
         end
     end

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Xavier Bardwell 2021-11-23

x = [-2.0000 -0.1130 -0.0545 0.0168 0.5409 0.5414 1.6444]

y = [50.1774 0.0007 0.0001 -0.0000 -0.0316 -0.0315 26.1672]

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Answer 1

Image Analyst 2021-11-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1594129-why-isn-t-my-y-value-changing#answer_838704

在 MATLAB Online 中打开

I think you are trying to do this:

% Demo by Image Analyst
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 22;
x = linspace(0, 2*pi, 400);
y = cos(x) + 0.3 * rand(1, length(x));
p1 = plot(x,y,'b-');
hold on;
rSQ = 0;
loopCounter = 1;
maxIterations = 100;
currentOrder = 1;
requiredRSquared = 0.95;
while rSQ < requiredRSquared && loopCounter < maxIterations
    fprintf('On iteration %d\n', loopCounter);
    coefficients = polyfit(x,y,currentOrder);
    yFitted = polyval(coefficients, x);
    yAVG = mean(yFitted);
    rSQTop = (yFitted - y).^2;
    rSQBot = (yFitted - yAVG).^2;
    rSQ = 1 - (sum(rSQTop) / sum(rSQBot));
    message = sprintf('On iteration %d rSQ = %f.  Order = %d', loopCounter, rSQ, currentOrder);
    fprintf('%s\n', message)
    if rSQ > requiredRSquared
        p2 = plot(x, yFitted, 'g-', 'LineWidth', 5);
    else
        p2 = plot(x, yFitted, 'r-', 'LineWidth', 5);
        currentOrder = currentOrder + 1;
    end
    grid on;
    title(message, 'FontSize', 18);
    g = gcf;
    g.WindowState = 'maximized';
    promptMessage = sprintf('Showing iteration %d.\nDo you want to Continue processing,\nor Quit processing?', loopCounter);
    titleBarCaption = 'Continue?';
    buttonText = questdlg(promptMessage, titleBarCaption, 'Continue', 'Quit', 'Continue');
    if contains(buttonText, 'Quit', 'IgnoreCase', true)
        break; % or break or continue.
    end
    loopCounter = loopCounter + 1;
    % Get rid of last plot.
    if rSQ < requiredRSquared
        delete(p2);
    end
end