public static DMatrixRMaj rotX( double ang, DMatrixRMaj R ) {
		if( R == null )
			R = new DMatrixRMaj( 3, 3 );

		setRotX( ang, R );

		return R;
	}
public static DMatrixRMaj rotX ( double ang , DMatrixRMaj R ) { if ( R == null ) R = new DMatrixRMaj ( 3 , 3 ) ; setRotX ( ang , R ) ; return R ; }
Creates a rotation matrix about the x-axis.

@param ang the angle it rotates a point by in radians.
@param R (Output) Optional storage for rotation matrix.  Modified.
@return The 3 by 3 rotation matrix.