Test NMS for issue

test.py

import numpy as np # version 1.16.1 and python 3.6.7

def nms_cpu_kernel(dets, scores, iou_threshold):

    x1 = dets[:, 0]
    y1 = dets[:, 1]
    x2 = dets[:, 2]
    y2 = dets[:, 3]

    areas = (x2 - x1) * (y2 - y1)

    order = scores.argsort()[::-1]

    ndets = dets.shape[0]
    suppressed = np.zeros(ndets)
    keep = []

    for i in range(ndets):
        i = order[i]
        if suppressed[i] == 1:
            continue
        keep.append(i)

        ix1 = x1[i]
        iy1 = y1[i]
        ix2 = x2[i]
        iy2 = y2[i]
        iarea = areas[i]

        for j in range(i + 1, ndets):
            j = order[j]
            if suppressed[j] == 1:
                continue
            xx1 = max(ix1, x1[j])
            yy1 = max(iy1, y1[j])
            xx2 = min(ix2, x2[j])
            yy2 = min(iy2, y2[j])

            w = max(0.0, xx2 - xx1)
            h = max(0.0, yy2 - yy1)
            inter = w * h
            
            ovr = inter / (iarea + areas[j] - inter)
            if ovr > iou_threshold:
                suppressed[j] = 1

    return keep

def nms(dets, thresh):
    x1 = dets[:, 0]
    y1 = dets[:, 1]
    x2 = dets[:, 2]
    y2 = dets[:, 3]
    scores = dets[:, 4]

    areas = (x2 - x1) * (y2 - y1)
    order = scores.argsort()[::-1]

    keep = []
    while order.size > 0:
        i = order[0]
        keep.append(i)
        xx1 = np.maximum(x1[i], x1[order[1:]])
        yy1 = np.maximum(y1[i], y1[order[1:]])
        xx2 = np.minimum(x2[i], x2[order[1:]])
        yy2 = np.minimum(y2[i], y2[order[1:]])

        w = np.maximum(0.0, xx2 - xx1)
        h = np.maximum(0.0, yy2 - yy1)
        inter = w * h
        ovr = inter / (areas[i] + areas[order[1:]] - inter)

        inds = np.where(ovr <= thresh)[0]
        order = order[inds + 1]

    return keep


if __name__ == '__main__':

    boxes = [[0.0, 0.0, 1.0, 1.0],
            [2.0, 1.0, 1.0, 2.0]]

    boxes = np.array(boxes)
    scores = np.array([1., 0.5])

    keep = nms_cpu_kernel(boxes, scores, 0.7)
    print(keep)

    print()

    # just putting in the function parameter format
    boxes = [[0.0, 0.0, 1.0, 1.0, 1.0],
            [2.0, 1.0, 1.0, 2.0, 0.5]]
    boxes = np.array(boxes)
    keep = nms(boxes, 0.7)
    print(keep)


# The code above outpus:
# test.py:43: RuntimeWarning: invalid value encountered in double_scalars
#   ovr = inter / (iarea + areas[j] - inter)
# [0, 1]
#
# test.py:71: RuntimeWarning: invalid value encountered in true_divide
#   ovr = inter / (areas[i] + areas[order[1:]] - inter)
# [0]