question: public static void CF6 ( double [ ] x , double [ ] f , double [ ] c , int nx ) { double sum1 = 0.0 ; double sum2 = 0.0 ; double yj ; for ( int j = 2 ; j <= nx ; j ++ ) { if ( j % 2 == 1 ) { yj = x [ j - 1 ] - 0.8 * x [ 0 ] * Math . cos ( 6.0 * PI * x [ 0 ] + j * PI / nx ) ; sum1 += yj * yj ; } else { yj = x [ j - 1 ] - 0.8 * x [ 0 ] * Math . sin ( 6.0 * PI * x [ 0 ] + j * PI / nx ) ; sum2 += yj * yj ; } } f [ 0 ] = x [ 0 ] + sum1 ; f [ 1 ] = ( 1.0 - x [ 0 ] ) * ( 1.0 - x [ 0 ] ) + sum2 ; c [ 0 ] = x [ 1 ] - 0.8 * x [ 0 ] * Math . sin ( 6.0 * x [ 0 ] * PI + 2.0 * PI / nx ) - MYSIGN ( ( x [ 0 ] - 0.5 ) * ( 1.0 - x [ 0 ] ) ) * Math . sqrt ( Math . abs ( ( x [ 0 ] - 0.5 ) * ( 1.0 - x [ 0 ] ) ) ) ; c [ 1 ] = x [ 3 ] - 0.8 * x [ 0 ] * Math . sin ( 6.0 * x [ 0 ] * PI + 4.0 * PI / nx ) - MYSIGN ( 0.25 * Math . sqrt ( 1 - x [ 0 ] ) - 0.5 * ( 1.0 - x [ 0 ] ) ) * Math . sqrt ( Math . abs ( 0.25 * Math . sqrt ( 1 - x [ 0 ] ) - 0.5 * ( 1.0 - x [ 0 ] ) ) ) ; }
target:  Evaluates the CF6 problem.