How to assign a vector to multiple values.

I have these lines of code:

function f = trick(t,x,M,K)
f = zeros(4,1);
f(1) = x(2);
f(2) = x(3);
Minvneg = -inv(M);
[f(3),f(4)] = Minvneg*K*[x(4) x(5)]';

I'm using this inside of a function called within the ode23 function where M and K are 2x2 matrices. the result of

Minvneg*K*[x(4) x(5)]'

should give a 2x1 column vector which I need to assign to f(3) and f(4) respectively.

I have tried doing this multiple ways except for making the matrix multiplication happen within double for loops which is terrable.

What is the best way to assign these values.

I think this would be very similar to doing this and it not working.

[a b] = [1 2]

One thing I tried but didn't work was:

delta=Minvneg*K*[x(4) x(5)]';
f(3)=delta(1);
f(4)=delta(2);

This just doesn't work within the ode23 function

If it helps, here is the code I am using to call this function:

clc; clear
figure
time = (0:.001:22.5)';
M = [1 2; 3 4];
K = [5 6; 7 8];
x0 = [0;0;0;0]; %[position,velocity]
[t1,x]=ode23(@(t1,x) trick(t1,x,M,K), time, x0);

plot(t1,x(:,1));
xlabel('Time(sec)');
ylabel('Displacement');
title('Stepped Response(Underdamped)');