problems using bisection method to find a maximum

Question

Mathew 2011-9-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16997-problems-using-bisection-method-to-find-a-maximum

while abs(a-b)>.001
c = (a + b)/2;
  if (abs(y_int(1,find(abs(((c./x_int)-1))<.0001))-maxP)<.001)
     break;
  elseif (y_int(1,(find(abs(((a./x_int)-1))))<.001) > y_int(1,(find(abs(((b./x_int)-1))))<.001))
      b=c;        
  else
     a=c;
    end
end

So, I want a and b to converge upon a max, and yet they always seem to go to the minimum in the domain i specify. I'm using a spline, not a specific equation. Just to clarify the if and elseif lines. The if line says, if the power that I get at point c is really close to the maximum Power then stop. The elseif line says, if the power at A is greater than the power at B, then make b equal to c, otherwise make a=c. Can anybody see whats wrong?

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Walter Roberson 2011-9-28

I recommend you calculate

t = abs(((c./x_int)-1));

right after you assign c in the loop, and that you then replace the occurrences of that expression with the variable.

I also recommend you switch to logical indexing instead of using find().

I think the code will come out cleaner, more readable, and faster.

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Answer 1

Mathew 2011-9-29

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/16997-problems-using-bisection-method-to-find-a-maximum#answer_22931

thank you Walter Robertson. After changing those few things and scratching my head for a few minutes, I figured that some of the brackets were in the wrong position.