- Use the Symbolic Toolbox with symbolic equations and use dsolve() or like routines to find a symbolic solution if possible. This would involve defining Aflow as a symbolic variable and solving for it
- Use iterative equations. Initialize Aflow to something (0 perhaps) and run a calculation using that value and use the results of the calculation to refine the Aflow value, repeating this process until Aflow stabilizes, indicating consistent equations
- Use an ODE routine such as ode45() or ode15s() or possibly bvp4c() depending what you are trying to do.
solving iterative equations in matlab
6 visualizzazioni (ultimi 30 giorni)
Mostra commenti meno recenti
For a heat exchanger modelling, I would like to give different equations into the Matlab, and solve the unknowns with respect to equations' relationship. For example these are different equations, and parameters:
. . .
rhogi=rhogo*Pin1g*Tout1g/(Pout1g*Tin1g);
rhog=0.5*(rhogo+rhogi);
Gg=m1g/**Aflow**;
Dh=4***Aflow**/n*pi*Do;
Redh=Gg*Dh/nug;
fo=(delpag-(Gg^2*(1/rhogo-1/rhogi)))*rhog*0.5*Dh/(L*Gg^2);
ratio=Redh/Red;
fo=f*ratio^-0.2; %f=0.046*Redh^-0.2
h=0.95*Ga*0.5*f*(power(Pra,-2/3));
ho=cpg*Gg*0.5*fo*(power(Prg,-2/3));
X=Do/D;
UAh=UA/(h*n*pi*D*L);UAho=UA/(ho.n.pi.Do*L);
UAho=1-Uah;
Adim=**Aflow**/n*D^2;
...
, and among them for example "Aflow" shall exist in three different equations; but in the first line, Matlab stops due to "undefined variable Aflow". I need Matlab to go over all the equations, and find Aflow itself. How can I handle this?
0 Commenti
Risposte (1)
Walter Roberson
il 6 Mar 2016
There are three approaches:
7 Commenti
Walter Roberson
il 6 Mar 2016
After you defined Do as being a symbol, you used
Do=1.2*D;
which redefined it in terms of the symbol D. It is now an expression rather than a symbol by itself, so it cannot be solved for.
Caution: you define
fo=(delpag-(Gg^2*(1/rhogo-1/rhogi)))*rhog*0.5*Dh/(L*Gg^2);
but a couple of lines later you have
fo=f*ratio^-0.2; %f=0.046*Redh^-0.2
which redefines fo as being completely different. There is no point in calculating the first expression if you are going to change the variable before even using it ?
Vedere anche
Categorie
Scopri di più su Calculus in Help Center e File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!