title: Julia : BLAS.gemm!() parameters
body: <p>I want to use the BLAS package. To do so, the meaning of the two first parameters of the <code>gemm()</code> function is not evident for me.
  What do the parameters <code>'N'</code> and <code>'T'</code> represent?</p>
  
  <pre><code> BLAS.gemm!('N', 'T', lr,  alpha, A, B, beta, C)
  </code></pre>
  
  <p>What is the difference between <code>BLAS.gemm</code> and <code>BLAS.gemm!</code> ? </p>