main/src/georegression/geometry/ConvertRotation3D_F64.java
private static double get( DMatrixRMaj M , int index ) {
		if( index < 0 ) {
			return -M.data[-index-1];
		} else {
			return M.data[index-1];
		}
	}
private static double get( DMatrixRMaj M , int index ) {
		if( index < 0 ) {
			return -M.data[-index-1];
		} else {
			return M.data[index-1];
		}
	}
If the index is negative it returns the negative of the value at -index.  Starts at 0