Solving four equations with four unknowns in MATLAB

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Meysam
Meysam 2014-11-26
评论： Meysam 2014-11-26
Hello every one. I need to find the coefficients R1-R4 in these four equations. Appreciate your comments and helps.
399.87=(34.78R1)*((8.52E-6)^R2)*(0.2025^R3)*(0.33^R4)
399.87=(52.3R1)*((1.9E-5)^R2)*(0.2025^R3)*(0.33^R4))
936.72=(57.5R1)*((1.9E-5)^R2)*(0.3009^R3)*(0.33^R4))
1129=(53R1)*((1.9E-5)^R2)*(0.335^R3)*(0.5^R4))
I tried this code but it didnt help:
equ1='((34.78R1)*((8.52E-6)^R2)*(0.2025^R3)*(0.33^R4))-399.87'
equ2='((52.3R1)*((1.9E-5)^R2)*(0.2025^R3)*(0.33^R4))-399.87'
equ3='((57.5R1)*((1.9E-5)^R2)*(0.3009^R3)*(0.33^R4))-936.72'
equ4='((53R1)*((1.9E-5)^R2)*(0.335^R3)*(0.5^R4))-1129'
sol=solve(equ1,equ2,equ3,equ4)
Am I using a wrong code or I didn't execute it in the correct way?
Thanks in advance.

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采纳的回答

John D'Errico
John D'Errico 2014-11-26
When you ask a question, it help that you add sufficient information for someone to know your problem without a guess. What did it do that you felt was wrong? If an error message was generated, then show the complete message.
I might point out that fragments like 34.78R1 are not valid syntax in MATLAB. Multiplication employs the * operator.
Beyond that, it seems clear that your equations form a linear system once they are logged. Since you have 4 equations in 4 unknowns, a linear system will yield an exact answer. So backslash would trivially suffice.
  1 个评论
Meysam
Meysam 2014-11-26
Thanks for the information and I'm sorry for not providing complete information. Here is the error that I received:
??? Error using ==> solve>getEqns at 182 ' (34.78R1)*((8.52E-6)^R2)*(0.2025^R3)*(0.33^R4))-399.87 ' is not a valid expression or equation.
Error in ==> solve at 67 [eqns,vars] = getEqns(varargin{:});
Error in ==> meysam at 8 sol=solve(equ1,equ2,equ3,equ4)
I guess I failed at inserting the equations in the correct format. I try to correct them.

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