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Asked by Kelly on 29 Mar 2013

I am trying to create a nested function, but I get an error saying that the variable that I've chosen is already being used even though that's the variable that I need as an input for my second function to compute the equation.

function [root,numit,err] = newton(x,tol,fx,ddx) err = abs(fx(x)); numit = 0; while(err > tol && numit < 1000); numit = numit + 1; x = x - fx(x)/ddx(x); err = abs(fx(x)); end

if (numit == 1000) disp('Maxed out on iterations.') err; end

root = x;

function root = x dx = 0.001; for i = 2:length(x)-1; fx = exp(cos(x) + sin(x)) - 2; dxf=(diff(2:i)-diff(1:(i-1)))/2*dx'; end

root = dxf(x); end end

root is my desired output and it is denoted by x. I keep getting an error about x being used as a variable and in the nested function in the same scope. What am I doing wrong?

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Answer by Azzi Abdelmalek on 29 Mar 2013

Edited by Azzi Abdelmalek on 29 Mar 2013

Change the name of your nested function, because you are using x as function name and variable

function root = new_name(x)

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Azzi Abdelmalek on 29 Mar 2013

You do not need to call the nested function, it's called by the main function. If your main function is correct, provide the values of `x,tol,fx,ddx` then call your function

[root,numit,err] = newton(x,tol,fx,ddx)

Kelly on 29 Mar 2013

Ok, I got all the computations to work correctly. Now I'm stuck on plotting. I'm creating a 1x2 and the first plot is just the exact derivative of the function and the second should be the numerical approximation.

clc; clear all; close all; % Equation 1 tol = 0.001; % for central difference dx == tol ns = 5; a = 0; b = 7;

fx = inline('exp(cos(x) + sin(x)) - 2'); ddx = inline('(exp(cos(x) + sin(x)))*(cos(x)-sin(x))');

% Incremental Search Method [nroots,low,high] = increm_mod(fx,a,b,ns,tol);

for j = 1:length(low) fprintf('\n') disp(['The First Equation has ',num2str(nroots),' roots.'])

fprintf('\n') fprintf('-----------------------------------------------------------------') fprintf('\n') disp('USING THE NEWTON-RAPHSON METHOD:') fprintf('\n')

% Newton Estimate guess = 2*(a + b)/3; [root_n(j),numit_n,err_n(j)] = newton(low(j),tol,fx,ddx); disp(['Root # ',num2str(j),' = ',num2str(root_n(j))]) disp(['Error # ',num2str(j),' = ',num2str(err_n(j))]) disp(['Number of Iterations # ',num2str(j),' = ',num2str(numit_n)]) fprintf('\n')

end

n = 0; ns = 100; dx = (b-a)/ns; for j = a:dx:b n = n+1; f_p(n) = fx(j); x_p(n) = j; end

figure(1) subplot(2,1,1) plot(x_p,f_p); hold on grid on plot(fx,dx,'ko')%%%%%%%% here's is my problem xlabel('x-values') ylabel('fx') title('Solution Using Newton-Raphson') subplot(2,1,2) plot(root_n,root_err,'ko') xlabel('x values') ylabel('my function')

I'm not sure if I'm plotting the right variables for the derivative because my function and derivative are inline functions.

Azzi Abdelmalek on 29 Mar 2013

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