MATLAB: Conversion to logical from sym is not possible

error matlab codeMATLABsymbolicSymbolic Math Toolbox

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.

Best Answer

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
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