Function 'solve' is working in Matlab 2014a but not in Matlab 2018a, what's possibly wrong?
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Hello, everyone!
I've been trying to run a code that I have to solve a 22 ode system in order to get the equillibrium points for the system. I'm using the function solve and I have tested my code in Matlab 2014a and it works, but when I want to run it in Matlab 2018a it gives me this error:
Error using sym/solve
Inconsistent output with 21 variables for input argument with 1 variables.
I'm not sure what's wrong with the code since it works in Matlab 2014a, and I think I understand what the error means, but I haven't figure out what's wrong with it. I checked previous questions about working with solve in Matlab 2018 or further version, and they are more about syntaxis than the error I'm having. I also just checked the code in Matlab Online, but it's the same as in Matlab 2018. If you could please help me out to figure this out, I'd be grateful. Here's the code:
syms x1 x2 x3 x4 x5 x6 x7 x9 x10 x11 x12 x13 x14 x15 x16 x17 x18 x19 x20 x21 x22
x8 = 180;%DVx8;
% Constants:
rBGU = 70;
rRBCU = 10;
rGGU = 20;
rPGUB = 35;
rHGPB = 155;
TI = 25;
TGm = 65;
rHGUB = 20;
FKIC = 0.30;
FPIC = 0.15;
FLIC = 0.40;
alpha = 0.0482;
beta = 0.931;
K = 0.00794;
M1 = 0.00747;
M2 = 0.0958;
gamma = 0.575;
Q0 = 6.33;
rMGmC = 9.1;
rPGmRB = 9.1;
% Volumenes:
VBVG = 3.5;
VBIG = 4.5;
VHG = 13.8;
VLG = 25.1;
VGG = 11.2;
VKG = 6.6;
VPVG = 10.4;
VPIG = 67.4;
VBI = 0.26;
VHI = 0.99;
VGI = 0.94;
VLI = 1.14;
VKI = 0.51;
VPVI = 0.74;
VPII = 6.74;
VGm = 11310;
QBG = 5.9;
QHG = 43.7;
QAG = 2.5;
QLG = 12.6;
QGG = 10.1;
QKG = 10.1;
QPG = 15.1;
QBI = 0.45;
QHI = 3.12;
QAI = 0.18;
QKI = 0.72;
QPI = 1.05;
QGI = 0.72;
QLI = 0.90;
TB = 2.1;
TPG = 5;
TPI = 20;
IPIB = 4.5;
GPIB = 117;
GmB = 1;
ILB = 21.43;
GLB = 101;
GHB=91.89;
IHB = 15.15;
MPGUI = 7.03 + 6.52*tanh(0.338*((x15/IPIB) - 5.82));
MPGUG = x8/GPIB;
rPGU = MPGUI*MPGUG*rPGUB;
MHGPGm = 2.7*tanh(0.39*(x19/GmB)) - x18;
MHGPG = 1.42 - 1.41*tanh(0.62*((x5/GLB) - 0.497));
rHGP = x16*MHGPGm+MHGPG*rHGPB;
MHGPIi = 1.21 - 1.14*tanh(1.66*((x12/ILB) - 0.89));
MHGUG = 5.66 + 5.66*tanh(2.44*((x5/GLB) - 1.48));
MHGUIi = 2*tanh(0.55*(x12/ILB));
rHGU = x17*MHGUG*rHGUB;
% if 0<=x(6)<460
rKGE = 71 + 71*tanh(0.11*(x6 - 460));
% else if x(6)>460
% rKGE = -330 + 0.872*x(6);
% end
% end
rPIRB=4.5;
XB=0.1928;
X = (x3^3.27)/((132^3.27) + 5.93*(x3^3.02));
Y = X^1.11;
Pinf = Y;
% if X > x(22)
S = ((M1*Y) + M2*(X-x22))*x20;
% else if X <= x(22)
% S = M1*Y*x20;
% end
% end
YB=XB^1.11;
SB=M1*YB*x20;
rPIR = (S/SB)*rPIRB;
rLIC = FLIC*(QAI*x10 + QGI*x11 + rPIR);
rKIC = FKIC*(QKI*x13);
rPIC = x15/(((1 - FPIC)/FPIC)*(1/QPI) - (TPI/VPII));
rPGmC = rMGmC*x19;
MPGmRG = 2.93 - 2.10*tanh(4.18*((x3/GHB) - 0.61));
MPGmRI = 1.31 - 0.61*tanh(1.06*((x10/IHB) - 0.47));
rPGmR = MPGmRG*MPGmRI*rPGmRB;
Gempt = 0;
I = 0;
dxdt = [(QBG*(x3 - x1) - (VBIG/TB)*(x1 - x2))/VBVG; % x(1) dGBV
((VBIG/TB)*(x1 - x2) - rBGU)/VBIG; % x(2) dGBI
(QBG*x1 + QLG*x5 + QKG*x6 + QPG*x7 - QHG*x3 - rRBCU)/VHG; % x(3) dGH
(QGG*(x3 - x4) - rGGU)/VGG; % x(4) dGG
(QAG*x3 + QGG*x4 - QLG*x5 + rHGP - rHGU)/VLG; % x(5) dGL
(QKG*(x3 - x6) - rKGE)/VKG; % x(6) dGK
(QPG*(x3 - x7) - (VPIG/TPG)*(x7 - x8))/VPVG; % x(7) dGPV
((VPIG/TPG)*(x7 - x8) - rPGU + Gempt)/VPIG; % x(8) dGPI
(QBI*(x10 - x9))/VBI; % x(9) dIB
(QBI*x9 + QLI*x12 + QKI*x13 + QPI*x14 - QHI*x10)/VHI; % x(10) dIH
(QGI*(x10 - x11))/VGI; % x(11) dIG
(QAI*x10 + QGI*x11 - QLI*x12 + rPIR - rLIC)/VLI; % x(12) dIL
(QKI*(x10 - x13) - rKIC)/VKI; % x(13) dIK
(QPI*(x10 - x14) - (VPII/TPI)*(x14 - x15))/VPVI; % x(14) dIPV
((VPII/TPI)*(x14 - x15) - rPIC + I)/VPII; % x(15) dIPI
(1/TI)*(MHGPIi - x16); % x(16) dM_HGPI
(1/TI)*(MHGUIi - x17); % x(17) dM_HGUI
(1/TGm)*(((MHGPGm - 1)/2) - x18); % x(18) df2
(rPGmR - rPGmC)/VGm; % x(19) dGm
K*(Q0 - x20) + gamma*x21 - S; % x(20) dQ
alpha*(Pinf - x21); % x(21) dP
beta*(X - x22) % x(22) dI
];
%[x1,x2,x3,x4,x5,x6,x7,x9,x10,x11,x12,x13,x14,x15,x16,x17,x18,x19,x20,x21,x22]=solve(dxdt(1)==0,x1,dxdt(2)==0,x2,dxdt(3)==0,x3,dxdt(4)==0,x4,dxdt(5)==0,x5,dxdt(6)==0,x6,dxdt(7)==0,x7,dxdt(9)==0,x9,dxdt(10)==0,x10,dxdt(11)==0,x11,dxdt(12)==0,x12,dxdt(13)==0,x13,dxdt(14)==0,x14,dxdt(15)==0,x15,dxdt(16)==0,x16,dxdt(17)==0,x17,dxdt(18)==0,x18,dxdt(19)==0,x19,dxdt(20)==0,x20,dxdt(21)==0,x21,dxdt(22)==0,x22)
[x1,x2,x3,x4,x5,x6,x7,x9,x10,x11,x12,x13,x14,x15,x16,x17,x18,x19,x20,x21,x22]=solve([dxdt(1)==0,dxdt(2)==0,dxdt(3)==0,dxdt(4)==0,dxdt(5)==0,dxdt(6)==0,dxdt(7)==0,dxdt(9)==0,dxdt(10)==0,dxdt(11)==0,dxdt(12)==0,dxdt(13)==0,dxdt(14)==0,dxdt(15)==0,dxdt(16)==0,dxdt(17)==0,dxdt(18)==0,dxdt(19)==0,dxdt(20)==0,dxdt(21)==0,dxdt(22)==0],[x1,x2,x3,x4,x5,x6,x7,x9,x10,x11,x12,x13,x14,x15,x16,x17,x18,x19,x20,x21,x22])
X = [x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15,x16,x17,x18,x19,x20,x21,x22];
% assignin('base','X',X);
X = vpa(X,4);
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