The Rotunda at the Guggenheim Museum in Manhattan is perhaps the perfect place for a retrospective because it is, by design, cyclical; one can see backward or forward from any vantage point. Add to that the space’s airy curves, linear columns, barely- there inclines and the gentle shadows cast by low walls and it’s a most fitting medium to showcase the work of Agnes Martin, an artist who, over a career spanning more than five decades, honed and refined her practice of studied abstractions and strikingly stark minimalist pieces.