how do i put iteration values into a vector?

Question

Robert 2013-12-7

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评论： Robert 2013-12-7

Hi, im creating a matlab function that uses the secant method to create an approximation, im trying to take the values that are calculated in my while loop and put them into one vector showing all the values computed at each iteration, i can get my final iterated value to be the first element in the vector but cant get the values calculated before to appear my while loop looks like this

xold=x0;
xa=x1-(f(x1)*(x1-xold))/(f(x1)-f(xold));
iter=0;
while abs(xa-xold)>=D;
    iter=iter+1;
    xnew=xa-(f(xa)*(xa-xold))/(f(xa)-f(xold));
    xold=xa;
    xa=xnew;
end

in this x0 and x1 are initial values, iter is the number of iterations and D is the tolerance level of the funtion

also where abouts in this function do i need to put the vector code to show the iterations?

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Answer 1

Wayne King 2013-12-7

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编辑：Wayne King 2013-12-7

在 MATLAB Online 中打开

I'm not sure from your post, which values you want to retain over the life of the while loop, I'm assuming xnew

I would set the iter to 1 because you can't index a vector from zero in MATLAB and then increment the iter loop counter at the end of the while loop.

Without knowing all your variables, I can't test this, but does the following work?

    xold=x0;
    xa=x1-(f(x1)*(x1-xold))/(f(x1)-f(xold));
    iter=1;
    X  = [];
    while abs(xa-xold)>=D;
        X(iter) =xa-(f(xa)*(xa-xold))/(f(xa)-f(xold));
        xold=xa;
        xa=xnew;
        iter=iter+1;
    end

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Wayne King 2013-12-7

I've edited my post slightly. Doesn't the above do what you want?

Robert 2013-12-7

Done it, thanks so much!!!!!!

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Answer 2

sixwwwwww 2013-12-7

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编辑：sixwwwwww 2013-12-7

在 MATLAB Online 中打开

X = 0;
xold=x0;
xa=x1-(f(x1)*(x1-xold))/(f(x1)-f(xold));
iter=0;
X(iter + 1) = xa;
while abs(xa-xold)>=D;
    iter=iter+1;      
    xnew=xa-(f(xa)*(xa-xold))/(f(xa)-f(xold));
    xold=xa;
    xa=xnew;
    X(iter + 1) = xa;
end