How to use Solver?

clear  dlc
%feed composition
z1=.5;
z2=.1;
z3=.15;
z4=.25;
 
%other given data
F=150;
PD=250;
T=10;
 
 
 
F=150;
 
%k-values from chart yi/xi
k1=56;
k2=0.65;
k3=0.175;
k4=0.055;
 
%total balances
 
syms x 
eqn=solve(k1*((F*z1)/(k1*x+150-x))+k2*((F*z2)/(k2*x+150-x))+k3*((F*z3)/(k3*x+150-x))+k4*((F*z4)/(k4*x+150-x))==1)
 

I'm trying to solve for x in the eqn but all i get is this:

eqn =
 
                                                                         150
root(z^3 - (151985*z^2)/231 + (2120672000*z)/17787 - 36140000000/5929, z, 1)
root(z^3 - (151985*z^2)/231 + (2120672000*z)/17787 - 36140000000/5929, z, 2)
root(z^3 - (151985*z^2)/231 + (2120672000*z)/17787 - 36140000000/5929, z, 3)

Very confused since I had defined my z constants and I am only looking for the x variable

Answer 1

[madhan ravi]

Use vpasolve()

[Rebecca Reyes]

well the thing is my z values are all constants. I only wanted to solve for the x value. For some reason, my z values became variables even though i defined them above.

[madhan ravi]

Well, they are not your variables, they are the roots of the solution not in explicit form . If you use the numerical solver vpasolve() it'll give those roots for you explicitly.

https://www.mathworks.com/help/symbolic/solve.html?searchHighlight=solve&s_tid=srchtitle#bue1gk5-2

[Rebecca Reyes]

I'm sorry I'm just so confused because I had inputted in the code that

z1=.5;

z2=.1;

z3=.15;

z4=.25;

Then when put in solver the z's became something else.

Which I did not want I just wanted to solve for x...

did the x become a z?

[madhan ravi]

Read the link.

[Rebecca Reyes]

I see what you are trying to tell me but i see that my approach is all wrong for what i need to get as an answer.

i redid my coding since my answer is supposed to be just one number 88.

I posted it on another post.

Thank you for your help.

[madhan ravi]

Wow , you just completely ignored what I told you and simply asked the same question.

%feed composition
z1=.5;
z2=.1;
z3=.15;
z4=.25;
 
%other given data
F=150;
PD=250;
T=10;
 
 
 
F=150;
 
%k-values from chart yi/xi
k1=56;
k2=0.65;
k3=0.175;
k4=0.055;
 
%total balances
 
syms x 
Eqn = k1*((F*z1)/(k1*x+150-x))+k2*((F*z2)/(k2*x+150-x))+k3*((F*z3)/(k3*x+150-x))+k4*((F*z4)/(k4*x+150-x))==1;
X = vpasolve(Eqn) % you can see 4 answers so if you're looking for the root in a certain range say 50 - 100 you can use the below line

X = 

X_in_the_range = vpasolve(Eqn, [50 100])

X_in_the_range = 

88.652321154384366746951471346875

subs(Eqn, X_in_the_range) % to check if it satisfies, ofcourse it's not an exact solution but a close match to what you're looking for

ans = 

Come on , was that hard for you ? The reason I suggested vpasolve() is that you can input the domain for the solver to look for. Please stop asking the same question multiple times just because you didn't understand. It's not encouraged in this forum. Volunteers spend some time in helping and instead of giving them a proper response OP's tend to ask another question simultaneously.