Errors while trying to solve a simple differential equation
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Why am I getting all these errors while solving this simple differential equation?
syms y t a b
eqn = diff(y,t,2) == a^2*y;
Dy = diff(y,t);
cond = [y(0)==b, Dy(0)==1];
ySol(t) = dsolve(eqn,cond)
??? Error using ==> sym.sym>checkindex at 2590
Index must be a positive integer or logical.
Error in ==> sym.sym>privformatscalar at 2540
checkindex(x);
Error in ==> sym.sym>privformat at 2524
s = privformatscalar(x);
Error in ==> sym.sym>sym.subsref at 1364
[inds{k},refs{k}] = privformat(inds{k});
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Respuestas (1)
Walter Roberson
el 19 de Oct. de 2017
You need
syms y(t)
You are currently just using y so MATLAB do not know that it is a function and thinks it is a constant. Constant differentiated gives 0
2 comentarios
Walter Roberson
el 19 de Oct. de 2017
You must be using a older version of MATLAB. Try
syms a b t
y = sym('y(t)');
y0 = subs(y,t,0);
Dy = diff(y,t);
Dy0 = subs(Dy, t, 0);
D2y = diff(Dy,t);
eqn = D2y == a^2*y;
cond = [y0 == b, Dy0 == 1];
ySol = dsolve(eqn, cond(1), cond(2))
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