Creating a Nested Function

2013 3 29
1 个回答
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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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回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-3-29
编辑：Azzi Abdelmalek 2013-3-29

0 个投票

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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Kelly
Kelly 2013-3-29
I did that and I didn't get an error. However when I used the command whos I didn't see two functions. Only the first function calls it's variables and runs. The second doesn't seem to be doing anything. Am I not"nesting" the functions correctly?
Azzi Abdelmalek
Azzi Abdelmalek 2013-3-29
编辑：Azzi Abdelmalek 2013-3-29
whos displays variables in base workspace, the variables inside any function are not displayed. each function has its own workspace
Azzi Abdelmalek
Azzi Abdelmalek 2013-3-29
Also, if the first function is working and you are not getting errors, means the second function is also working
Kelly
Kelly 2013-3-29
Ok, but when I go to plot the functions do I need to call both functions or just the main? The main function is the newton raphson method for finding roots and the whole purpose of this nested function is to adapt the newton method to use the central difference method to numerically derive the roots.
Azzi Abdelmalek
Azzi Abdelmalek 2013-3-29
编辑：Azzi Abdelmalek 2013-3-29
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
Kelly 2013-3-29
编辑：Azzi Abdelmalek 2013-3-29
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
Azzi Abdelmalek 2013-3-29
If the answer helped, accept the answer and post a new question.

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Kelly
Kelly
2013-3-29

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