Interpolator that tends to (but never reaches) specified asymptotic value. Easing factor specifies how quickly it should approach the asymptote.

TangentialInterpolator.java

import android.view.animation.Interpolator;

public class TangentialInterpolator implements Interpolator {

    private float asymptote = 1f;
    private float easing = 1f;

    public TangentialInterpolator(float asymptote, float easing) {
        this.asymptote = asymptote;
        this.easing = easing;
    }

    @Override
    public float getInterpolation(float input) {
        return asymptote * onPiByTwoScale(tanInverse(input));
    }

    private float onPiByTwoScale(float value) {
        return (float) (value / (Math.PI / 2));
    }

    private float tanInverse(float value) {
        return (float) Math.atan(easing * value);
    }
}