Undefined Function or variable..​.NewtonRal​phson

Please help! This is the error I am receiving, "Undefined function or variable 'y_value'.

Error in seventh (line 39) while abs(y_value) > accuracy"

And below is the code function x_value = newtonraphson(x0,accuracy)

...

x0 = 10;

accuracy = 1e-10;

x_value = x0;

%subfunction 1

function y_value = find_y(x_value)

y_value = 3*(x_value)^3-15*(x_value)^2-20*(x_value)+50;

%y_value = log(x_value)-x_value+3

end

%subfunction 2

function diff = differentiate_y(x_value)

diff = 9*(x_value)-30*x_value-20;

%diff = 1/x

end

 while abs(y_value) > accuracy

     xprev = x_value;

    x_value = xprev - (y_value)/diff; % where diff is f', the derivative

fprintf('Current x value %d, Current y value %f, Root Approximation %g',xprev,y_value,x_value); 

 end

disp('The root is: ');

root = x_value;

end

Answer 1

[Julia]

Hi,

y_value is the output of your first subfunction.

You define the subfunction

function y_value = find_y(x_value)

...
end

and then you have to call it:

y_value = find_y(x_value);

The same holds for diff. You also should update y_value otherwise you will get an endless loop.

But I don't understand why you have the function newtonraphson() with input parameters x0 and accuracy and then the first thing you do is to define x0 and accuracy in the code for this function.