[V,D] = eig(sym([1 -1; 2 4]))to find eigenvalues and eigenvectors: The columns of V are the eigenvectors, the diagonal elements of D are the eigenvalues.
[y1,y2] = dsolve('Dy1 = 1*y1+(-1)*y2', 'Dy2 = 2*y1+4*y2', 't')as explained in Using Matlab for Systems of ODEs.
f = inline('[1 -1;2 4]*y','t','y')and use Plotting a Phase Portrait of an Autonomous System.