I have a problem associate with the graphic of the streamline function developed by Zarei-Doudeji and Samani (2016) in the paper “Capture zone of a multi-well system in bounded rectangular-shaped aquifers: modeling and application”. These authors propose an analytical solution for the capture zone of a multi-wellsystem in a bounded confined aquifer.The solution is based in the equipotential and the streamline functions in a dimensionless form (equations (11) and (12) in the paper). Programming in MATLAB the equipotential and the streamline functions(streamline function showed below), and when I plot the streamline function (red line in the figure attached) near to the wells, the streamline have a rare behavior (see the figure attached). I think that is a problem with the atan(*) function. Anybody know any reason and solution for this?