question: protected static Dfp atanInternal ( final Dfp a ) { Dfp y = new Dfp ( a ) ; Dfp x = new Dfp ( y ) ; Dfp py = new Dfp ( y ) ; for ( int i = 3 ; i < 90 ; i += 2 ) { x = x . multiply ( a ) ; x = x . multiply ( a ) ; x = x . negate ( ) ; y = y . add ( x . divide ( i ) ) ; if ( y . equals ( py ) ) { break ; } py = new Dfp ( y ) ; } return y ; }
target:  computes the arc-tangent of the argument.