// 随机产生散点数据
NSUInteger i;
for ( i = 0 ; i < nums ; i++ ) {
x [i] = i ;
y1 [i] = ( nums * 10 )*( rand ()/( float ) RAND_MAX );
y2 [i] = ( nums * 10 )*( rand ()/( float ) RAND_MAX );
}
NSUInteger i;
for ( i = 0 ; i < nums ; i++ ) {
x [i] = i ;
y1 [i] = ( nums * 10 )*( rand ()/( float ) RAND_MAX );
y2 [i] = ( nums * 10 )*( rand ()/( float ) RAND_MAX );
}