A problem with a "Recursive Function"

Question

onsagerian 2020-7-9

0
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https://ww2.mathworks.cn/matlabcentral/answers/562586-a-problem-with-a-recursive-function

评论： onsagerian 2020-7-10

The following is a simple program using a "recursive function". As indicated, the code is designed to take the input value 5 initially and solve the recursive relation to get the expression for "a". The answer is supposed to be a=2*b^(1/3), but the program produces a=2b. Actually, it gives the same output which is 2b for any "n" (n>=5), and simply gives 1 for any "n" (provided that n<5). As you can see, It solves b=0.5*a*Recursive(m-2) (The value of m decreases by 2).

Are there any points I missed in understanding the logic I constructed? I would greatly appreciate it if you would help me to redisign the code so that the program can work properly.

n=5;
x=Recursive(n);
disp(x)
function r=Recursive(m)
syms a b
  if(m<1)
     r=1;
  else
     temp=0.5*a*Recursive(m-2);  
     eqn=b==temp;
     E=solve(eqn,a);
     r=E;
  end
end

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Answer 1

Alan Stevens 2020-7-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/562586-a-problem-with-a-recursive-function#answer_464117

编辑：Alan Stevens 2020-7-10

在 MATLAB Online 中打开

You could try the following:

syms a b
n=5;
eqn=b==Recursive(n);
     a=solve(eqn,a);
disp(a)
function r=Recursive(m)
syms a
  if(m<1)
     r=1;
  else
     r=0.5*a*Recursive(m-2);  
  end
end