MATLAB: Subscripted assignment dimension mismatch : When using ode45

Question

Why does MATLAB throw this error? I'm multiplying a 4*3 matrix with a 3*1 matrix to obtain 4*1 matrix(d). my differentiation equation is dy/dt=1/2*d which should give me a 4*1 matrix.

w1=0.0181844;
w2=0.128911;
w3=0;
w=[w1;w2;w3];
E1=0.704416;
E2=-0.0616284;
E3=0.0616284;
E4=0.704416;
y=[E1;E2;E3;E4];
M=[E4 -E3 E2;E3 E4 -E1;-E2 E1 E4;-E1 -E2 -E3];
d=M*w;
tspan=[0 0.0001 1];
y0=[0;0;0;0];
a=1/2;
options = odeset('AbsTol',1e-8);
[t,y]=ode45(@(t,y) EuRodFunc(t,y,a,d),tspan,y0);
function dydt = EuRodFunc(t,y,a,d)
dydt(1)=a.*d;

Answer 1

function dydt = EuRodFunc(t,y,a,d)
dydt = zeros(4,1);
dydt = a.*d;