plz help me check the this error. Warning: Unable to solve symbolically. Returning a numeric solution using vpasolve.

plz help me to check the error,

I dont know anything wrong.

thank you

%define the functon\\
clear
syms y1 y2 y z t t1 t2 h z1 z2
S1 = -y*exp(-10/(z+273));
S2 = y*1000*exp(-10/(z+273))-10*(z-20);
SS1 = y2 - y1 - h*subs(S1,{y z},[y2 z2]);
SS2 = z2 -z1 - h*subs(S2,{y z},[y2 z2]);
EQN1 = SS1 ==0
Y = solve(EQN1, y2);
EQN2 = SS2 ==0
Z = solve(EQN2, z2);

%solve the system\\

H=0.2;
T=0:H:10;


YN(1)=1;
ZN(1)=15;


fprintf('------------------------------------------\n');
fprintf(' S.No.   h\t\t y1\t\t\t  y2\t\n');
fprintf('------------------------------------------\n');
fprintf('  1.0 \t  %4.4f \t \t %4.4f \t %4.4f \n', T(1), YN(1), ZN(1));

for i = 2: length(T)
    EQ1 = subs(EQN1,{y1 z1 h t}, [YN(i-1) ZN(i-1) H T(i)]);
    EQ2 = subs(EQN2,{y1 z1 h t}, [YN(i-1) ZN(i-1) H T(i)]);
    [solx,soly] = solve(EQ1,EQ2);
    YN(i) = double(solx);
    ZN(i) = double(solx);
    fprintf(' %4.1f\t %4.4f\t\t $r.rf\t\t %4.4f\t\n',i,T(i),YN(i),ZN(i));
end

fprintf('===============================\n');

%define the analytical function\\
%%


%Solve the analytical solution\\

[time,p]=ode45(@fun1,[0,10],[1 15]);

%Plot the solution\\

TIT=['MATLAB Solution;']; XL='t'; YL='y';
figure('units','normalized','Position', [0.1 0.1 0.7 0.8])
plot(T,YN,'b','Linewidth',2)
hold on
plot(time,p(:,1),'r','Linewidth',2)

plot(T,ZN,'-ob','Linewidth',2)
hold on
plot(time,p(:,2),'-or','Linewidth',2)
hold on
grid on
box on
xlabel(XL)
ylabel(YL)
title(TIT)
grid on
set(gca,'FontSize',20)
legend('CA1','CA2','CB1','CB2','Location','NorthEast')
ST=char(datetime('now'));
print(['Plot1.png'],'-dpng')

function Dp=fun1(t,p)
y=p(1);z=p(2);
Dp = [ -y*exp(-10/(z+273)); y*1000*exp(-10/(z+273))-10*(z-20)];
% Dp=Dp';
end

Answer 1

[Ameer Hamza]

This is not an error. It is just a warning by MATLAB that it is not able to find a symbolic solution, so it is returning the numeric solution. If you only care about the value of the solution, then this should not be an issue. You can suppress this warning by changing line 31 in your code to

[solx,soly] = vpasolve(EQ1,EQ2);