Function Intersection using Newton's Method
显示 更早的评论
Hi everyone, I'm trying to write a function that finds a point at
which two functions f(x) and g(x) intersect, i.e., f(x) = g(x). I'm using
Newton's Method and making and h(x)=f(x)-g(x) and h'(x) as well, but I'm not getting the right x-value. Please help me debug my code!
% function x = fgIntersect(f, df, g, dg, x0, tol, maxIter)
h=f(x0)-g(x0)
dh=df(x0)-dg(x0)
k=1;
while k<=maxIter
x=x0-h/dh;
if abs(x-x0)<tol*abs(x)
return
end
x0=x;
k=k+1;
end
end
2 个评论
Matt J
2012-11-19
Give us example data that let's us reproduce the failure.
采纳的回答
Matt J
2012-11-19
0 个投票
You're not updating h and dh within your loop.
4 个评论
SB
2012-11-19
Matt J
2012-11-19
As new points x are generated in the loop, you want h and dh to be evaluated at those points.
SB
2012-11-19
f = @(x) exp(x) - 3;
df = @(x) exp(x);
g = @(x) sqrt(x);
dg = @(x) .5*x^(-.5);
x = fgIntersect(f, df, g, dg, 1, 1e-6, 50)
p1 = [1 -2 3 -8];
p2 = [1 -3 2 -4];
f = @(x) polyval(p1,x);
df = @(x) polyval(polyder(p1),x);
g = @(x) polyval(p2,x);
dg = @(x) polyval(polyder(p2),x);
x = fgIntersect(f, df, g, dg, 2, 1e-6, 50)
function x = fgIntersect(f, df, g, dg, x0, tol, maxIter)
h=f(x0)-g(x0);
dh=df(x0)-dg(x0);
k=1;
while k<=maxIter
x=x0-h/dh;
if abs(x-x0)<tol*abs(x)
return
end
x0=x;
h = f(x0)-g(x0);
dh = df(x0)-dg(x0);
k=k+1;
end
end
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Translated by 
