Conversion to logical from sym is not possible

Hi everyone, can you help me fix this problem
1. This is my matlab code

clc 
clear all

syms v u w 
w= exp(v)/(v^2 + u)
diffw = diff(w,v)
simplify(diffw)

eq = v^2 - 2*v + u == 0

D1 = 4-4*u < 0
D2 = 4-4*u == 0
D3 = 4-4*u > 0

if D1 < 0
    fprintf('No solution')
    solve(D1,u)
elseif D == 0
   fprintf('Dual solution')
   solveD(D2,u)
else D > 0
    fprintf('Two solution')
    solve(D3,u)
end

prompt1='u=';
u= input(prompt1);
xSol=solve(eq,v)
subs(xSol,u)

Error : Conversion to logical from sym is not possible

2.I don't know matlab can solve > 0 or < 0 with no u(number) so i put another code and it have the same error

clc 
clear all

syms v u w 
w= exp(v)/(v^2 + u)
diffw = diff(w,v)
simplify(diffw)

eq = v^2 - 2*v + u == 0

prompt1='u=';
u= input(prompt1);

D1 = 4-4*u < 0
D2 = 4-4*u == 0
D3 = 4-4*u > 0

if D1 < 0
    fprintf('No solution')
    solve(D1,u)
elseif D == 0
   fprintf('Dual solution')
   solveD(D2,u)
else D > 0
    fprintf('Two solution')
    solve(D3,u)
end

xSol=solve(eq,v)
subs(xSol,u)

Error :When I put u=1
D1 =
  logical
   0
D2 =
  logical
   1
D3 =
  logical
   0
Unrecognized function or variable 'D'.
elseif D == 0

Thank you very much.

Answer 1

[madhan ravi]

4 * u
% ^ 

Give assumptions for u:

assume(u > 0)
D1 = isAlways(4-4*u < 0)
D2 = isAlways(4-4*u == 0)
D3 = isAlways(4-4*u > 0)

And in if block remove the comparator.

if D1 
    fprintf('No solution')
    solve(D1,u)
elseif D2
   fprintf('Dual solution')
   solveD(D2,u)
else D3 
    fprintf('Two solution')
    solve(D3,u)
end

[Nguyen Tien Dung]

Sorry I fixed it, but it seems like my error is in the if command

[Nguyen Tien Dung]

Soryy if i don't put u and just use command if

D1 = 4-4*u < 0

D2 = 4-4*u == 0

D3 = 4-4*u > 0

if D1

fprintf('No solution')

solve(D1,u)

elseif D2

fprintf('Dual solution')

solve(D2,u)

else D3

fprintf('Two solution')

solve(D3,u)

end

can matlab solve

u>1

u=1

u<1

Thanks for your help :))