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matlabnumerical-methods

fixed point iteration in matlab

So I am meant to write a Matlab function that has a starting guess p and tolerance e as inputs and outputs the number of iterations n and final fixed point approx pn satisfying abs(pn-pn-1) <= e for a given function g. Here is what I currently have:

function f = fixed(p,e)
i=1;
pn=g(p);
while (abs(pn - p) <= e)
    pn = g(p)
    i=i+1;
    p=pn
end
end

But I'm not sure where I'm going wrong. Do I need to include another if statement in the case that the absolute difference is >e? What else would I include in such a statement?

Solution

  • Try this:

    function f = fixed(p,e)
i=1;
pn=g(p);
while (abs(pn - p) <= e)
    p = pn
    pn=g(p)
    i=i+1;
end
f = pn
end

    I think you were comparing p and pn after the p=pn statement causing an early exit.