How to perform a \$\dfrac{1}{s+a}\$ type integration in MATLAB?
I'm not an expert but look at this page: http://ctms.engin.umich.edu/CTMS/index.php?example=Introduction&amp;section=SystemModeling    

In the command prompt, you can write as follows: 

s = tf('s');
integrator = 1/(s+a) ;


Then simply use it in your expression.