Multiple Equations Solver Problem

Question

Alexander 2014-11-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/164027-multiple-equations-solver-problem

回答： Alexander 2014-11-24

All variables are known except c, Prise, Treflection and Pabs

 syms c
 Treflection = 2*L_drivepipe/c;
 Prise = c*rho*V_crit*Treflection/Taction;
 Pabs = Pstat_closing + Prise;
 if (Air_in_Account == false)
        eq1 = c == sqrt(1/(rho*(1/Ev_water+(s)*D_drivepipe/EYoung/Thick_drivepipe)));
 else
        eq1 = c == sqrt(1/(rho*(cv1/Ev_water+cv2/gamma/Pabs+  (s)*D_drivepipe/EYoung/Thick_drivepipe)));
 end
 [c] = solve(eq1,c);
 c = eval(c);   
 Prise = eval(Prise); 
 Pabs = eval(Pabs); 
 Treflection = eval(Treflection);

Matlab calculates values for Pabs and Prise. But does not give a value for c while actually Pabs and Prise are functions of c. I know that we can solve back to know the value of c out of the result of Pabs or Prise but that doesn't seem good programming to me. Making a set of equations was also an option but my matlab only returned a matrix with the variables in it without values. Can someone help?

This is an easy solve situation and I can't understand that since a week my matlab is unable to give good outputs.

Thanks in advance, A