未定义的函数或变量“ w”

Question

I'm trying to solve an ODE for a school project, and I'm running into a problem with one variable. Wondering if I could get some help. I'm using ODE15s solver.

options = odeset('RelTol',2.22045e-14, 'AbsTol', 1e-6);
[T,Y] = ode15s(@odeHMCase5,[0,200],[4.3,5.1,3,0,422],options);

The variable in question is part of a block of conditional statements, when debugging it does show up in the workspace.

%define G as a global variable
global G

%Define ec
if z(5) < 453
    ec = 0;
else
    ec = 1;
end

if (ec == 1) & (G == false)
    G = true;
elseif (ec == 1) & (G == true)
    G = true;
elseif (ec == 0) & (G == true)
    G = true;
elseif (ec == 0) & (G == false)
    G = false;
end

if G == false
    w = 0;
elseif (G == true) & (z(5) >= 433)
    w = 1;
elseif (G == true) & (z(5) < 433)
    w = 0;
    G = false;
end

In addition the conditional operators &&, when running, MATLAB throws up this error ,

Operands to the || and && operators must be convertible to logical scalar values.

Changing to & seems to be the only way around it.

Any help would be greatly appreciated.

Answer 1

The first problem (" Operands to the || and && operators must be convertible to logical scalar values. ") is pretty easy to solve. In the scope of if statement conditions, you must use the double logical operators ( && or || ):

if (ec == 1) & (G == false)  % WRONG
if (ec == 1) && (G == false) % CORRECT

The undefined variable w error is due to the fact that your last if statement ends with an elseif and no else clause is defined. Therefore, when none of the specified conditions is evaluated to true , no value is assigned variable w :

if G == false % THIS CAN ALSO BE REWRITTEN AS: if (~G)
    w = 0;
elseif (G == true) && (z(5) >= 433) % FIX THE LOGICAL OPERATOR
    w = 1;
elseif (G == true) && (z(5) < 433) % FIX THE LOGICAL OPERATOR
    w = 0;
    G = false;
else
    w = ?; % WRITE SOMETHING HERE
end

The statement above could be also simplified as follows, and this should fix the issue unless I misunderstood what you're trying to accomplish:

if (G)
    if (z(5) >= 433)
        w = 1;
    else
        w = 0;
        G = false;
    end
else
    w = 0;
end