title: Substracting every nth element of a matrix from every ith element from another matrix
body: <p>I have two matrices</p>
  
  <pre><code>A = [a,b,c,d,e,f,g,h,i,j,k,l]
  B = [w,x,y,z]
  </code></pre>
  
  <p>I want to substract like <code>[a,e,i]</code> from <code>w</code> and <code>[b,,f,j]</code> from <code>x</code> like that. 
  All these letters are floats. The results will be in an array.</p>
  
  <p>Could you assist how to substract every <code>n</code>-th element ofa matrix from every <code>i</code>-th element from another matrix?</p>