How to solve non linear equation for one variable?

Question

Farhan Ashraf 2018-4-24

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https://ww2.mathworks.cn/matlabcentral/answers/397068-how-to-solve-non-linear-equation-for-one-variable

评论： Farhan Ashraf 2018-4-24

Hi, I am trying to solve a non-linear equation for one variable but it's not working. Can somebody help me in this regards? your help would be highly appreciated. Thanks

 if
temp=[24 78 139 194 297 397];
yieldstress=[45 36 37 33 30 28];
syms DD positive
solve((6.046.*sqrt(DD))./(1e6)+(9.79.*(1-((-4.7872e-5.*temp).*(log(6.667e-4./(286.*sqrt(DD))))).^(2/3)).^(3/2)).*(3.06) == yieldstress);
end

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Answer 1

njj1 2018-4-24

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https://ww2.mathworks.cn/matlabcentral/answers/397068-how-to-solve-non-linear-equation-for-one-variable#answer_316932

编辑：njj1 2018-4-24

在 MATLAB Online 中打开

If you want to solve for multiple values of temp and yieldstress, you will have to use a for loop.

for i=1:numel(temp)
  for j=1:numel(yieldstress)
    out{i,j} = solve((6.046.*sqrt(DD))./(1e6)+(9.79.*(1-((-4.7872e-5.*temp(i)).*(log(6.667e-4./(286.*sqrt(DD))))).^(2/3)).^(3/2)).*(3.06) == yieldstress(j));
  end
end

The output variable "out" contains the values of DD that solve the equations as symbolic numbers (so long as the equation can be solved), and these can be evaluated using the command eval().

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njj1 2018-4-24

在 MATLAB Online 中打开

If you type in the code exactly as I have then it should work. It will take a while but it should work.

for i=1:numel(temp)
  for j=1:numel(yieldstress)
    out{i,j} = solve((6.046.*sqrt(DD))./(1e6)+(9.79.*(1-((-4.7872e-5.*temp(i)).*(log(6.667e-4./(286.*sqrt(DD))))).^(2/3)).^(3/2)).*(3.06) == yieldstress(j));
    dd(i,j) = eval(out{i,j}); %DO NOT put DD here
  end
end

FYI, I've run this code for the first few values of temp and yieldstress that you posted above, and Matlab is not able to find an explicit solution.

Farhan Ashraf 2018-4-24