I am trying to assign only positive integers to a variable.

I have an equation which returns positive and negative real and imaginary numbers. I have already separated the real part and assigned it to a variable "w", which now returns positive and negative real numbers. I only need the positive numbers assigned to "w" so that when "h" is solved the result is only positive real numbers.

L=15.7; 
l=11.6; 
Wab=20; 
Wbd=40;
Mab = Wab/32.2; 
Mbd = Wbd/32.2; 
Wbd2=(Wbd/(L-1)); 
d=2.58; 
OB=L-l-d; 
BD=d+OB; 
Wbo=Wbd2*OB; 
Wod=Wbd2*d; 
delta=d*0.95; 
syms Wc
eqn = (((11.6/2)+1.52)*20)+((((15.6-11.6)/2)-1.52)*Wbo)-((d/2)*Wod)-(delta*Wc)==0;
S = solve(eqn);
Wc = eval(S) 

Wc = 56.8458

Mc = Wc/32.2; 
D=490*(1/32.2); 

syms w
eqn = Mc*D==(4*(w.^3));
V = solve(eqn); 

w1 = eval(V); 
w = real(w1)

w = 3×1

1.8867 -0.9434 -0.9434

h=2*w

h = 3×1

3.7734 -1.8867 -1.8867

[Star Strider]

Specify ‘w’ to be real, and then request 'ReturnConditions' on the evaluation to understand under what conditions ‘w’ will be real:

syms w real

eqn = Mc*D==(4*(w.^3));

V = solve(eqn, 'ReturnConditions',1)

That is likely the best you can do.

L=15.7; 
l=11.6; 
Wab=20; 
Wbd=40;
Mab = Wab/32.2; 
Mbd = Wbd/32.2; 
Wbd2=(Wbd/(L-1)); 
d=2.58; 
OB=L-l-d; 
BD=d+OB; 
Wbo=Wbd2*OB; 
Wod=Wbd2*d; 
delta=d*0.95; 
syms Wc real
eqn = (((11.6/2)+1.52)*20)+((((15.6-11.6)/2)-1.52)*Wbo)-((d/2)*Wod)-(delta*Wc)==0;
S = solve(eqn)

S = 

% Wc = eval(S) 
Mc = Wc/32.2; 
D=490*(1/32.2); 

syms w real
eqn = Mc*D==(4*(w.^3));
V = solve(eqn, 'ReturnConditions',1) 

V = struct with fields:
             w: [3×1 sym]
    parameters: [1×0 sym]
    conditions: [3×1 sym]

V.w

ans = 

V.conditions

ans = 

% w1 = eval(V)
% w = real(w1)
h=2*w

h = 

I leave you to explore those conditions at your leisure.

.

Answer 1

[Vilém Frynta]

Not sure if I understand correctly, but if you want to ignore the negative values, you can do:

w = [1.8 -0.9 -0.9]'    % your values

w = 3×1

1.8000 -0.9000 -0.9000

w = w(w>0)              % only positive values

w = 1.8000

Hope I helped, otherwise feel free to correct me or describe your problem.