main/src/georegression/geometry/ConvertRotation3D_F64.java
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.