title: how can i solve the error: operator -: nonconformant arguments
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  <p>this is the problem that is about digital signal
  professor does not want let me use for function
  so i tried using sum function
  this is what i tried:</p>
  <pre><code>&gt;&gt; n = -10:10;k = -5:5;x = sum(exp(-abs(k)) .* ((n-2*k)==0));
  </code></pre>
  <p>[error: operator -: nonconformant arguments][3] (op1 is 1x21, op2 is 1x11)</p>
  <p>i know why it makes error but i don't know how to sum with two variables...</p>