Solving 8 equations with 8 unknowns using FSOLVE

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radwan alfahel
radwan alfahel 2020-12-10
评论： Alex Sha 2020-12-10
I have 8 equations with 8 unknowns as shown bellow. please how can I solve them and find the unkowns. I tried FSOLVE coding and it showed an error (Error using fsolve (line 298). Objective function is returning undefined values at initial point. FSOLVE cannot continue.). So, please could you help me to find the issue.
function F = radwan(x)
jw1=1.787;
jw2=3.0375;
DHv=2257; %kj/kg (40.65 kj/mol)
Tbf1=35;
Tbf2=45.6;
Tbp1=10.9;
Tbp2=12.7;
Q1=17000.763;
Q2=26000.778;
C1=0.680046641;
C2=0.754098;
hm1=1;
hm2=1;
F(1)=x(1)*(Tbf1-x(2))-Q1;
F(2)=hm1*(x(2)-x(3))+jw1*DHv-Q1;
F(3)=x(4)*(x(3)-Tbp1)-Q1;
F(4)= x(5)*(Tbf2-x(6))-Q2;
F(5)=hm2*(x(6)-x(7))+jw2*DHv -Q2;
F(6)=x(8)*(x(7)-Tbp2)-Q2;
F(7)=C1*((exp(-6.4313+(1882/x(2)))/exp(-6.4313+(1882/x(6))))^0.14)-(x(5)/x(1));
F(8)=C2*((exp(-6.4313+(1882/x(3)))/exp(-6.4313+(1882/x(7))))^0.14)-(x(8)/x(4));

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采纳的回答

Walter Roberson
Walter Roberson 2020-12-10
you have divisions by x1, x2, x3, x4, x6, and x7. Your code would fail if the initial values for any of those are 0.
  2 个评论
Matt J
Matt J 2020-12-10
编辑：Matt J 2020-12-10
Or, rewrite the final equations as,
F(7)=x(1)*C1*((exp(-6.4313+(1882/x(2)))/exp(-6.4313+(1882/x(6))))^0.14)-x(5);
F(8)=x(4)*C2*((exp(-6.4313+(1882/x(3)))/exp(-6.4313+(1882/x(7))))^0.14)-x(8);
Alex Sha
Alex Sha 2020-12-10
Matt's suggestion is an effective method,If doing like that, there will be multi-solutions:
1:
x1: 152.742230393022
x2: -76.3036188895187
x3: -13043.8076188895
x4: -1.30227068244721
x5: 3.40351026683942
x6: -7593.80048993739
x7: -26738.9409899374
x8: -0.971932077354813
fevl:
-1.81898940354586E-11
-1.81898940354586E-11
1.81898940354586E-11
7.27595761418343E-12
1.09139364212751E-11
2.5465851649642E-11
-3.99680288865056E-15
3.59712259978551E-14
2:
x1: 0.53037478392545
x2: -32019.2444989045
x3: -44986.7484989045
x4: -0.377814476247884
x5: 0.359028482663491
x6: -72374.2197510973
x7: -91519.3602510973
x8: -0.284061977067628
fevl:
1.81898940354586E-11
0
-1.09139364212751E-11
-1.09139364212751E-11
-3.63797880709171E-12
-5.45696821063757E-11
-3.17379456049594E-12
-6.14297501755345E-12

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