hi I have a code to plot the results of a for- loop I would though like this to start at my first value of x

% EMTH171

% script using newtons method

clear

clc

close all

% function

f = @(x) 3*x.^4 + 7*x.^3 - 4*x.^2 - 10*x + 1/5;

% derivative

d = @(x) 12*x.^3 + 21*x.^2 - 8*x - 10;

% test value

x = -3;

z = x;

N = 20;

tol = 1e-4;

for ii = 1 : N

x = x - f(x)/d(x);

position = ii + 1;

appArray(position, 1) = x;

x = x;

residual = abs(f(x));

residualArray(position, 1) = residual;

lastvalue = appArray(ii, 1);

diff = abs(x - lastvalue);

absoluteArray(ii, 1) = diff;

if (diff < tol) && (residual < tol)

break

end

anArray(ii,1) = x;

end

fprintf('%.4f\n' ,anArray);

plot(anArray)

Answer 1

[Alan Stevens]

Change your loop slightly:

for  ii = 1 : N
    anArray(ii) = x;  %%%%%%%%%%%%%%
    x = x - f(x)/d(x);
    position = ii + 1;
    appArray(position, 1) = x;
    x = x;
    residual = abs(f(x));
    residualArray(position, 1) = residual;
    lastvalue = appArray(ii, 1);
    diff = abs(x - lastvalue);
    absoluteArray(ii, 1) = diff;
    if (diff < tol) && (residual < tol)
        break 
    end
   % anArray(position,1) = x;
end