MATLAB: Bisection help PLS HELP ME

bisectionMATLABmatrixmatrix multiplication

I have this code for a bisection method but I cant seem to figure out why it wont work I just get this error

every thing else is given

any help is appreciated thanks

Error using  * 
Incorrect dimensions for matrix multiplication. Check that the
number of columns in the first matrix matches the number of rows in
the second matrix. To perform elementwise multiplication, use '.*'.
Error in bisectiona>f (line 65)
x=(2*Fo/wn.^2-w.^2)*sin((wn-w/2)*t)*sin((wn+w/2)*t);
Error in bisectiona (line 14)
    f_left = f(x_left);
function bisectiona
% Bisection method: Used for solving an equation, and finding an
% approximate solution to an equation.
    clc
    % The number of bisection steps
    n = 32;
    % define the initial interval
    a = 41;
    b = 69;
    fprintf('\n initial interval [%g, %g] \n total bisection steps %d\n', a,b,n);
    % Check that a root does exist in the chosen interval
    x_left = a;
    x_right = b;
    f_left = f(x_left);
    f_right = f(x_right);
    if f_left*f_right > 0
    end
    % Bisection: The method
    for i=1:n
        if f_left == 0
            % The exact root of the equation is found at the lower bound
            % of the chosen interval

            fprintf('\n stage %g root %g with zero absolute error \n',i,x_left);
            return;
        end
        if f_right==0
            % The exact root of the equation is found at the upper bound
            % of the chosen interval
            fprintf('\n stage %g root %g with zero absolute error \n',i,x_right);
            return
        end
        % Bisection method: The process
        x_mid = (x_left+x_right)/2.0;
        f_mid = f(x_mid);
        if f_left*f_mid <= 0
            % There is a root in [x_left,x_mid]
            x_right = x_mid;
            f_right = f_mid;
        end
        if f_left*f_mid > 0
            % There is a root in [x_mid,x_right]
            x_left = x_mid;
            f_left = f_mid;
        end
        % Calculate the approximate root for current step
        root = (x_left+x_right)/2.0;
        % Calculate the absolute error for current step
        abs_err=(x_right-x_left)/2.0;
        fprintf('\n stage %g root %g absolute error < %g \n',i,root,abs_err);
    end
    %check satisfaction of equation at end of process
    residual = f(root);
    fprintf('\n final residual = %g \n',residual);
end
    %Created Subfunction to define equation f(x)
function f_value = f(~)
k = 2800;
m = 0.6705;
Fo = 2.0535;
t = 9.177;
x = 0.0253;
w = 77:0.1:80;
wn= sqrt(k/m);
fo= Fo/m;
x=(2*Fo/wn.^2-w.^2)*sin((wn-w/2)*t)*sin((wn+w/2)*t);
f_value = x;
end

Best Answer

"but I cant seem to figure out why it wont work I just get this error"

function f_value=f(~)
k = 2800;
m = 0.6705;
Fo = 2.0535;
t = 9.177;
x = 0.0253;
w = 77:0.1:80;
wn= sqrt(k/m);
fo= Fo/m;
x=(2*Fo/wn^2-w.^2).*sin((wn-w./2)*t).*sin((wn+w./2).*t);
f_value = x;
end

Main Script:

    clc
    clear all;
    close all;
    % approximate solution to an equation.
    % The number of bisection steps
    n = 32;
    % define the initial interval
    a = 41;
    b = 69;
    fprintf('\n initial interval [%g, %g] \n total bisection steps %d\n', a,b,n);
    % Check that a root does exist in the chosen interval
    x_left = a;
    x_right = b;
    f_left=f(x_left);
    f_right=f(x_right);
    if (f_left.*f_right)> 0
    end
    % Bisection: The method
    for i=1:n
        if f_left == 0
            % The exact root of the equation is found at the lower bound
            % of the chosen interval

            fprintf('\n stage %g root %g with zero absolute error \n',i,x_left);
            return;
        end
        if f_right==0
            % The exact root of the equation is found at the upper bound
            % of the chosen interval
            fprintf('\n stage %g root %g with zero absolute error \n',i,x_right);
            return
        end
        % Bisection method: The process
        x_mid = (x_left+x_right)/2.0;
        f_mid = f(x_mid);
        if f_left.*f_mid <= 0
            % There is a root in [x_left,x_mid]
            x_right = x_mid;
            f_right = f_mid;
        end
        if f_left.*f_mid > 0
            % There is a root in [x_mid,x_right]
            x_left = x_mid;
            f_left = f_mid;
        end
        % Calculate the approximate root for current step
        root = (x_left+x_right)/2.0;
        % Calculate the absolute error for current step
        abs_err=(x_right-x_left)/2.0;
        fprintf('\n stage %g root %g absolute error < %g \n',i,root,abs_err);
    end
    %check satisfaction of equation at end of process
    residual = f(root);
    fprintf('\n final residual = %g \n',residual);

Command Window:

Please note: I removed the code errors only.

Related Solutions

MATLAB: Error using function matlab

You do not call the function bisection

Your function f does not have access to the variables defined in the script. f would need to be a nested function using shared variables -- and you need to nest inside a function, not inside a script.

For example,

function driver
    k=1007.564; %stiffness (N/m)
    m=98.668; %mass (kg)
    F_0=108.764; %applied force magnitude (N)
    
    bisection(@f);      %call your function
    
    function f_value = f(x) %x=omega
        %this is a nested function that shares variables
      f_value = (v_0/om_n)*sin(om_n*t) + (x_0-((f_0)/(om_n)^2-(x)^2))*cos(om_n*t) + ((f_0)/(om_n)^2-(x)^2)*cos(x*t);
    end
end
function bisection(f)
  stuff
end

MATLAB: Error in the function

clear;
clc;

Get rid of these. As written your file is a script file with local functions, and the only code that is executed when you run this script are these two lines. If you start your file with the "function calculate" line, it becomes a function file and calling it will call the calculate function.

function calculate

If you want your calculate function to return anything you need to define it to return something. As written calculate takes no input arguments and returns no output arguments. See this documentation page for how to define a function to return one or more output arguments.

k=1007.564; %stiffness (N/m)
m=98.668; %mass (kg)
F_0=108.764; %applied force magnitude (N)
x_0=-0.02; %initial displacement (m)
v_0=0.1; %initial velocity (m/s)
t=4.54; %time (s)
x_1=0.0386; %displacement (m)
om_n=sqrt(k/m);
f_0=F_0/m;
x=0; %omega
    %calling function
    bisection(@f);

bisection accepts one input argument and returns no output arguments. You need to define it to return an output then call it to assign that output to something in order to get it to work the way you described wanting it to work.

I snipped the rest of the code because I didn't see anything at a quick glance that needed modification. [There was at least one typo in the comments, but that doesn't affect the results of the code.]

Best Answer

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MATLAB: Error in the function

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