/*&nbsp;---------------------------------------------------------------------------
&nbsp;&nbsp;&nbsp;produces&nbsp;a&nbsp;list&nbsp;with&nbsp;the&nbsp;two&nbsp;partial&nbsp;derivatives&nbsp;of&nbsp;f
&nbsp;&nbsp;&nbsp;---------------------------------------------------------------------------&nbsp;*/
&nbsp;&nbsp;&nbsp;eqs:[diff(f,x),diff(f,y)],
/*&nbsp;---------------------------------------------------------------------------
&nbsp;&nbsp;&nbsp;produces&nbsp;a&nbsp;list&nbsp;of&nbsp;unknowns
&nbsp;&nbsp;&n