On the continuity of principal eigenvalues for boundary value problems with indefinite weight function with respect to radius of balls in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="$\mathbb{R}^N$"><mml:mrow><mml:msup><mml:mi>ℝ</mml:mi><mml:mrow><mml:mi>N</mml:mi></mml:mrow></mml:msup></mml:mrow></mml:math>
International journal of mathematics and mathematical sciences