# Solving a Nonlinear Equation using Newton-Raphson Method

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It's required to solve that equation: f(x) = x.^3 - 0.165*x.^2 + 3.993*10.^-4 using Newton-Raphson Method with initial guess (x0 = 0.05) to 3 iterations and also, plot that function.

Please help me with the code (i have MATLAB R2010a) ... I want the code to be with steps and iterations and if possible calculate the error also, please

##### 2 Comments

Syed nisar Abbas
on 5 Jul 2021

### Accepted Answer

Bruno Pop-Stefanov
on 25 Nov 2013

Edited: Brewster
on 25 Nov 2013

x = 0.05;

x_old = 100;

x_true = 0.0623776;

iter = 0;

while abs(x_old-x) > 10^-3 && x ~= 0

x_old = x;

x = x - (x^3 - 0.165*x^2 + 3.993*10^-4)/(3*x^2 - 0.33*x);

iter = iter + 1;

fprintf('Iteration %d: x=%.20f, err=%.20f\n', iter, x, x_true-x);

pause;

end

You can plot the function with, for example:

x = -10:0.01:10;

f = x.^3 - 0.165*x.^2 + 3.993*10^-4;

figure;

plot(f)

grid on

##### 6 Comments

Cesar Castro
on 21 Sep 2021

It did not work , May you help me, please? My F = x(1)^4+x(2)^4+2*x(1)^2*x(2)^2-4*x(1)+3 I Know the root is 1.

I do not know why, it did not work. Thanks in advance.

### More Answers (10)

Dhruv Bhavsar
on 28 Aug 2020

- Solve the system of non-linear equations.

x^2 + y^2 = 2z

x^2 + z^2 =1/3

x^2 + y^2 + z^2 = 1

using Newton’s method having tolerance = 10^(−5) and maximum iterations upto 20

%Function NewtonRaphson_nl() is given below.

fn = @(v) [v(1)^2+v(2)^2-2*v(3) ; v(1)^2+v(3)^2-(1/3);v(1)^2+v(2)^2+v(3)^2-1];

jacob_fn = @(v) [2*v(1) 2*v(2) -2 ; 2*v(1) 0 2*v(3) ; 2*v(1) 2*v(2) 2*v(3)];

error = 10^-5 ;

v = [1 ;1 ;0.1] ;

no_itr = 20 ;

[point,no_itr,error_out]=NewtonRaphson_nl(v,fn,jacob_fn,no_itr,error)

NewtonRaphson_nl_print(v,fn,jacob_fn,no_itr,error);

# OUTPUT.

Functions Below.

function [v1 , no_itr, norm1] = NewtonRaphson_nl(v,fn,jacob_fn,no_itr,error)

% nargin = no. of input arguments

if nargin <5 , no_itr = 20 ; end

if nargin <4 , error = 10^-5;no_itr = 20 ; end

if nargin <3 ,no_itr = 20;error = 10^-5; v = [1;1;1]; end

v1 = v;

fnv1 = feval(fn,v1);

i = 0;

while true

jacob_fnv1 = feval(jacob_fn,v1);

H = jacob_fnv1\fnv1;

v1 = v1 - H;

fnv1 = feval(fn,v1);

i = i + 1 ;

norm1 = norm(fnv1);

if i > no_itr && norm1 < error, break , end

%if norm(fnv1) < error , break , end

end

end

function [v1 , no_itr, norm1] = NewtonRaphson_nl_print(v,fn,jacob_fn,no_itr,error)

v1 = v;

fnv1 = feval(fn,v1);

i = 0;

fprintf(' Iteration| x | y | z | Error | \n')

while true

norm1 = norm(fnv1);

fprintf('%10d |%10.4f| %10.4f | %10.4f| %10.4d |\n',i,v1(1),v1(2),v1(3),norm1)

jacob_fnv1 = feval(jacob_fn,v1);

H = jacob_fnv1\fnv1;

v1 = v1 - H;

fnv1 = feval(fn,v1);

i = i + 1 ;

norm1 = norm(fnv1);

if i > no_itr && norm1 < error, break , end

%if norm(fnv1) < error , break , end

end

end

This covers answer to your question and also queries for some comments I read in this thread.

##### 2 Comments

Upendra Kumar
on 13 Apr 2021

Pourya Alinezhad
on 25 Nov 2013

you can use the following line of code;

x = fzero(@(x)x.^3 - 0.165*x.^2 + 3.993*10.^-4,0.05)

Eduardo
on 13 Apr 2014

Hello,

I am trying to make a program using the Newton-Raphson method for complex equations, but I am in a infinite loop.

If I change the expression,

x = x - (x^3 - 0.165*x^2 + 3.993*10^-4)/(3*x^2 - 0.33*x);

For this:

x = x - (sqrt(-x))/(-0.5.*(1./sqrt(-x)));

The algorithm does not work.

how can I use a complex equation in this case ??

Thank you very much.

##### 0 Comments

Valdes Corleone
on 1 Sep 2018

##### 0 Comments

Sayeed
on 21 Oct 2018

##### 1 Comment

madhan ravi
on 21 Oct 2018

Please ask a separate question question because it would make this thread unrelated

Sayeed
on 21 Oct 2018

Thanks, I did. Can u help with that?

https://se.mathworks.com/matlabcentral/answers/425183-code-for-equation-with-ln

##### 0 Comments

ali raza
on 28 Mar 2021

function [v1 , no_itr, norm1] = NewtonRaphson_nl(v,fn,jacob_fn,no_itr,error) % nargin = no. of input arguments if nargin <5 , no_itr = 20 ; end if nargin <4 , error = 10^-5;no_itr = 20 ; end if nargin <3 ,no_itr = 20;error = 10^-5; v = [1;1;1]; end

v1 = v;

fnv1 = feval(fn,v1);

i = 0;

while true

jacob_fnv1 = feval(jacob_fn,v1);

H = jacob_fnv1\fnv1;

v1 = v1 - H;

fnv1 = feval(fn,v1);

i = i + 1 ;

norm1 = norm(fnv1);

if i > no_itr && norm1 < error, break , end

%if norm(fnv1) < error , break , end

end

end

function [v1 , no_itr, norm1] = NewtonRaphson_nl_print(v,fn,jacob_fn,no_itr,error) v1 = v; fnv1 = feval(fn,v1); i = 0; fprintf(' Iteration| x | y | z | Error | \n') while true norm1 = norm(fnv1); fprintf('%10d %10.4f %10.4f | %10.4f| %10.4d |\n',i,v1(1),v1(2),v1(3),norm1) jacob_fnv1 = feval(jacob_fn,v1); H = jacob_fnv1\fnv1; v1 = v1 - H; fnv1 = feval(fn,v1); i = i + 1 ; norm1 = norm(fnv1); if i > no_itr && norm1 < error, break , end %if norm(fnv1) < error , break , end

end

end

##### 0 Comments

Mohamed Hakim
on 21 May 2021

Edited: Walter Roberson
on 12 Feb 2022

function NewtonRaphsonMethod

%Implmentaton of Newton-Raphson method to determine a solution.

%to approximate solution to x = cos(x), we let f(x) = x - cos(x)

i = 1;

p0 = 0.5*pi; %initial conditions

N = 100; %maximum number of iterations

error = 0.0001; %precision required

syms 'x'

f(x) = x - cos(x); %function we are solving

df = diff(f); %differential of f(x)

while i <= N

p = p0 - (f(p0)/df(p0)); %Newton-Raphson method

if (abs(p - p0)/abs(p)) < error %stopping criterion when difference between iterations is below tolerance

fprintf('Solution is %f \n', double(p))

return

end

i = i + 1;

p0 = p; %update p0

end

fprintf('Solution did not coverge within %d iterations at a required precision of %d \n', N, error) %error for non-convergence within N iterations

end

##### 0 Comments

Christine Joy Africa
on 23 Mar 2022

function NewtonRaphsonMethod

%Implmentaton of Newton-Raphson method to determine a solution.

%to approximate solution to x = cos(x), we let f(x) = x - cos(x)

i = 1;

p0 = 0.5*pi; %initial conditions

N = 100; %maximum number of iterations

error = 0.0001; %precision required

syms 'x'

f(x) = x - cos(x); %function we are solving

df = diff(f); %differential of f(x)

while i <= N

p = p0 - (f(p0)/df(p0)); %Newton-Raphson method

if (abs(p - p0)/abs(p)) < error %stopping criterion when difference between iterations is below tolerance

fprintf('Solution is %f \n', double(p))

return

end

i = i + 1;

p0 = p; %update p0

end

fprintf('Solution did not coverge within %d iterations at a required precision of %d \n', N, error) %error for non-convergence within N iterations

end

##### 0 Comments

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