title: Defining Matrices with argument in mathematica
body: <p>I have a matrix A=[1-x, 2;1 3-x].  How do I define this in Mathematica so I can do things like </p>
  
  <p>SchurDecomposition(A[1])</p>
  
  <p>and </p>
  
  <p>f[x_]:= maximum eigenvalue of A[x_];  then plot f for x in [-1,1]. </p>
  
  <p>Thanks in advance. </p>