DimensionMismatchError: exp, dimensions were (s^-1)
<p>I writing a program with brian simulator and i get this error :</p>

<p><code>DimensionMismatchError</code>: exp, dimensions were (<code>s^-1</code>) </p>

<p>The line that I am getting the error is : </p>

<pre><code>I=(Vt-El)/ (1-(exp(-(S.spiketimes[0][i-1]_S.spiketimes[0][i])/tau_a)))
</code></pre>

<p>I can't understand the problem</p>
