Plotting data within while loop,help

No plot displays even though the function works, at the end of the function

use this in command window

w = 25.5; E = 50*10^3;I = 30*10^3; L = 600;
dy = @(x) (w/(120*E*I*L))*((-5*x^4)+(6*L^2*x^2)-(L^4))
[xmax fx eapprox iteration]=bisect(dy,0.1,600,2)

%writing function for Bisection Method 

function [root,fx,eapprox,iteration]= bisect(funct, xlower, xupper, deserr)
iteration = 0; xr = xlower;  eapprox = 100;
%m = mass = 80 kg 
% v = velocity,36m/s 
% g = gravitational acceleration = 9.81 m/s^2
%x1 = lower guess (given 0.1)
%xu = upper guess (given 0.2) 
% t = time  = 4s 
%root = root finding (cd, mass, time, etc)
%eap = approximate relative error 
% es = desired relative error, <=2%
%fx = function value at root
hold on
while (1)  
 
   xold = xr;  % previous xr value for comparision for approximate relative error
xr = (xlower +xupper)/2;   % solve mean for interval 
iteration = iteration +1; % increment for iterations 

if xr ~= 0  % if mean doesnt equal 0 
    eapprox = abs(xr -xold / xr)*100; % solving approximate relative error for xl and xu 
    
end %end of first if statement
test = funct(x1ower)*funct(xr); %testing to see if interval needs to be moved left or right

if test > 0 % positive 
    xlower = xr;
    
else
    if test < 0 %negative
    xupper = xr; 
     else
        eapprox = 0; % if there is 0 approximate error that means the root is found
    end %end of second if statement

    if eapprox <= deser
     break,end %end of if statements


end %end of while loop
%disp(output)
plot(iteration,xr,'ro')
plot(iteration,eapprox, 'b')

root = xr,
end %end of fucntion

[Bob Thompson]

There seem to be a number of issues with this code, even before getting to the lack of plots. For example you have x1ower instead of xlower, and deser is undefined. Could you please double check that your copy here is correct?

[Alexa Shumaker]

I am not good at coding to begin with. xlower is fixed. Not changing deser i its required to keep it like that.

I really just need help on plotting in while loop.

function [root,fx,eapprox,iteration]= bisect(funct, xlower, xupper, deserr)

iteration = 0; xr = xlower; eapprox = 100;

%m = mass = 80 kg

% v = velocity,36m/s

% g = gravitational acceleration = 9.81 m/s^2

%xl = lower guess (given 0.1)

%xu = upper guess (given 0.2)

% t = time = 4s

%root = root finding (cd, mass, time, etc)

%eap = approximate relative error

% es = desired relative error, <=2%

%fx = function value at root

hold on

while (1)

xold = xr; % previous xr value for comparision for approximate relative error

xr = (xlower +xupper)/2; % solve mean for interval

iteration = iteration +1; % increment for iterations

if xr ~= 0 % if mean doesnt equal 0

eapprox = abs(xr -xold / xr)*100; % solving approximate relative error for xl and xu

end %end of first if statement

test = funct(xlower)*funct(xr); %testing to see if interval needs to be moved left or right

if test > 0 % positive

xlower = xr;

else

if test < 0 %negative

xupper = xr;

else

eapprox = 0; % if there is 0 approximate error that means the root is found

end %end of second if statement

if eapprox <= deser

break,end %end of if statements

end %end of while loop

%disp(output)

plot(iteration,xr,'ro')

plot(iteration,eapprox, 'b')

root = xr,

end %end of fucntion

[Bob Thompson]

Ah, I see. deser should be deserr with two 'r's.

Does the loop break for you? When I ran with the inputs you posted I reached an iteration of ~25000 before I aborted because the eapprox and root converged at 2.6733e4 and ~268.32 respectively.

The plotting appears to work fine though, though it was effectively two straight lines, mostly due to the scale.

If you're looking to do plots like this I generally prefer using indexing within the loop, and then a single plot command outside, as it allows for more options in plot configurations. It would look something like this:

iteration = 1;
x = xlower
while (1)
    xold = x(iteration);
    iteration = iteration + 1;
    x(iteration) = mean([xlower xupper]);
    % Replace all xr with x(iteration)
    ...
    % Also index eapprox with eapprox(iteration)
end
figure(1)
plot([1:iteration],x,'ro');
figure(2)
plot([1:iteration],eapprox,'b');

[Alexa Shumaker]

this is the input and output I get when I run it

>> w = 25.5; E = 50*10^3;I = 30*10^3; L = 600;

dy = @(x) (w/(120*E*I*L))*((-5*x^4)+(6*L^2*x^2)-(L^4))

[xmax fx eapprox iteration]=bisect(dy,0.1,600,2)

dy =

function_handle with value:

@(x)(w/(120*E*I*L))*((-5*x^4)+(6*L^2*x^2)-(L^4))

xmax =

267.2430

fx =

-1.9801e-04

eapprox =

1.7537

iteration =

7

[Bob Thompson]

There is an order of operations error in the calculation of eapprox.

eapprox = abs(xr -xold / xr)*100; % is in the posting
eapprox = abs((xr -xold) / xr)*100; % Should be

See my edits to my previous comment for notes about plotting.

Answer 1

[Harshit Jain]

You can use "drawnow" if you want to plot data in each iteration of while loop.

w = 25.5; E = 50*10^3;I = 30*10^3; L = 600;
dy = @(x) (w/(120*E*I*L))*((-5*x^4)+(6*L^2*x^2)-(L^4))
[xmax fx eapprox iteration]=bisect(dy,0.1,600,2)
%writing function for Bisection Method 
function [root,fx,eapprox,iteration]= bisect(funct, xlower, xupper, deserr)
    iteration = 0; xr = xlower;  eapprox = 100;
    %m = mass = 80 kg 
    % v = velocity,36m/s 
    % g = gravitational acceleration = 9.81 m/s^2
    %x1 = lower guess (given 0.1)
    %xu = upper guess (given 0.2) 
    % t = time  = 4s 
    %root = root finding (cd, mass, time, etc)
    %eap = approximate relative error 
    % es = desired relative error, <=2%
    %fx = function value at root
    figure
    hold on
    while (1)  
        xold = xr;  % previous xr value for comparision for approximate relative error
        xr = (xlower +xupper)/2;   % solve mean for interval 
        iteration = iteration +1; % increment for iterations 
        if xr ~= 0  % if mean doesnt equal 0 
            eapprox = abs(xr -xold / xr)*100; % solving approximate relative error for xl and xu 

        end %end of first if statement
        test = funct(xlower)*funct(xr); %testing to see if interval needs to be moved left or right
        if test > 0 % positive 
            xlower = xr;

        else
            if test < 0 %negative
            xupper = xr; 
             else
                eapprox = 0; % if there is 0 approximate error that means the root is found
            end %end of second if statement
            if eapprox <= deserr
             break,end %end of if statements
        end %end of while loop
        %disp(xr)
        plot(iteration,xr,'ro')
        %hold on
        plot(iteration,eapprox, 'bo')
        root = xr;
        drawnow;
    end %end of fucntion
end

Answer 2

[Armin Motallebi]

clear

clc

%User Defined Properties

serialPort = 'COM7'; % define COM port #

plotTitle = 'Serial Data Log'; % plot title

xLabel = 'Elapsed Time (s)'; % x-axis label

yLabel = 'Acceleration'; % y-axis label

plotGrid = 'on'; % 'off' to turn off grid

min = -1.5; % set y-min

max = 2.5; % set y-max

scrollWidth = 10; % display period in plot, plot entire data log if <= 0

delay = .0000001; % make sure sample faster than resolution

%Define Function Variables

time = 0;

data = zeros(3,1);

count = 0;

%Set up Plot

plotGraph = plot(time,data(1,:),'-r',...

'LineWidth',2,...

'MarkerFaceColor','w',...

'MarkerSize',2);

hold on

plotGraph1 = plot(time,data(2,:),'-m',...

'LineWidth',1,...

'MarkerFaceColor','w',...

'MarkerSize',2);

hold on

plotGraph2 = plot(time,data(3,:),'-b',...

'LineWidth',1,...

'MarkerFaceColor','w',...

'MarkerSize',2);

title(plotTitle,'FontSize',25);

xlabel(xLabel,'FontSize',15);

ylabel(yLabel,'FontSize',15);

axis([0 10 min max]);

grid(plotGrid);

%Open Serial COM Port

s = serial(serialPort, 'BaudRate', 115200)

disp('Close Plot to End Session');

fopen(s);

tic

while ishandle(plotGraph) && ishandle(plotGraph2) && ishandle(plotGraph1) %Loop when Plot is Active

dat = fscanf(s,'%f'); %Read Data from Serial as Float

if(~isempty(dat) && isfloat(dat)) %Make sure Data Type is Correct

count = count + 1;

time(count) = toc; %Extract Elapsed Time in seconds

data(:,count) = dat(:,1); %Extract 1st Data Element

%Set Axis according to Scroll Width

if(scrollWidth > 0)

set(plotGraph,'XData',time(time > time(count)-scrollWidth),...

'YData', data(3,time > time(count)-scrollWidth));

set(plotGraph1,'XData',time(time > time(count)-scrollWidth),...

'YData', data(2,time > time(count)-scrollWidth));

set(plotGraph2,'XData',time(time > time(count)-scrollWidth),...

'YData', data(1,time > time(count)-scrollWidth));

axis([time(count)-scrollWidth time(count) min max]);

else

set(plotGraph,'XData',time,'YData',data(3,:));

set(plotGraph1,'XData',time,'YData',data(2,:));

set(plotGraph2,'XData',time,'YData',data(1,:));

axis([0 time(count) min max]);

end

%Allow MATLAB to Update Plot

pause(delay);

end

end

%Close Serial COM Port and Delete useless Variables

fclose(s);

clear count dat delay max min plotGraph plotGraph1 plotGraph2 plotGrid...

plotTitle s scrollWidth serialPort xLabel yLabel;

disp('Session Terminated');

prompt = 'Export Data? [Y/N]: ';

str = input(prompt,'s');

if str == 'Y' || strcmp(str, ' Y') || str == 'y' || strcmp(str, ' y')

%export data

csvwrite('accelData.txt',data);

type accelData.txt;

else

end

clear str prompt;