Hi everyone,
When I run the PMG model by xtpmg command, I have a problem the iteration log likelihood not concave like this

Iteration 0: log likelihood = -3467.8035 (not concave)
Iteration 1: log likelihood = -3467.4309 (not concave)
Iteration 2: log likelihood = -3467.4142 (not concave)
Iteration 3: log likelihood = -3467.4078 (not concave)
Iteration 4: log likelihood = -3467.4078 (not concave)
Iteration 5: log likelihood = -3467.4078 (not concave)
Iteration 6: log likelihood = -3467.4078 (not concave)
Iteration 7: log likelihood = -3467.4078 (not concave)
Iteration 8: log likelihood = -3467.4078 (not concave)
Iteration 9: log likelihood = -3467.4078 (not concave)
Iteration 10: log likelihood = -3467.4078 (not concave)
Iteration 11: log likelihood = -3467.4078 (not concave)
Iteration 12: log likelihood = -3467.4078 (not concave)
Iteration 13: log likelihood = -3467.4078 (not concave)
Iteration 14: log likelihood = -3467.4078 (not concave)
Iteration 15: log likelihood = -3467.4078 (not concave)
Iteration 16: log likelihood = -3467.4078 (not concave)
Iteration 17: log likelihood = -3467.4078 (not concave)
Iteration 18: log likelihood = -3467.4078 (not concave)
Iteration 19: log likelihood = -3467.4078 (not concave)
Iteration 20: log likelihood = -3467.4078 (not concave)
Iteration 21: log likelihood = -3467.4078 (not concave)
Iteration 22: log likelihood = -3467.4078 (not concave)
Iteration 23: log likelihood = -3467.4078 (not concave)
Iteration 24: log likelihood = -3467.4078 (not concave)
Iteration 25: log likelihood = -3467.4078 (not concave)
Iteration 26: log likelihood = -3467.4078 (not concave)
Iteration 27: log likelihood = -3467.4078 (not concave)
Iteration 28: log likelihood = -3467.4078 (not concave)
Iteration 29: log likelihood = -3467.4078 (not concave)
Iteration 30: log likelihood = -3467.4078 (not concave)
Iteration 31: log likelihood = -3467.4078 (not concave)
Iteration 32: log likelihood = -3467.4078 (not concave)
Iteration 33: log likelihood = -3467.4078 (not concave)
Iteration 34: log likelihood = -3467.4078 (not concave)
Iteration 35: log likelihood = -3467.4078 (not concave)
Iteration 36: log likelihood = -3467.4078 (not concave)
Iteration 37: log likelihood = -3467.4078 (not concave)
Iteration 38: log likelihood = -3467.4078 (not concave)
Iteration 39: log likelihood = -3467.4078 (not concave)
Iteration 40: log likelihood = -3467.4078 (not concave)
Iteration 41: log likelihood = -3467.4078 (not concave)
Iteration 42: log likelihood = -3467.4078 (not concave)
Iteration 43: log likelihood = -3467.4078 (not concave)
Iteration 44: log likelihood = -3467.4078 (not concave)
Iteration 45: log likelihood = -3467.4078 (not concave)
Iteration 46: log likelihood = -3467.4078 (not concave)
Iteration 47: log likelihood = -3467.4078 (not concave)
Iteration 48: log likelihood = -3467.4078 (not concave)
Iteration 49: log likelihood = -3467.4078 (not concave)
Iteration 50: log likelihood = -3467.4078 (not concave)
Iteration 51: log likelihood = -3467.4078 (not concave)
Iteration 52: log likelihood = -3467.4078 (not concave)
Iteration 53: log likelihood = -3467.4078 (not concave)
Iteration 54: log likelihood = -3467.4078 (not concave)
Iteration 55: log likelihood = -3467.4078 (not concave)
Iteration 56: log likelihood = -3467.4078 (not concave)
Iteration 57: log likelihood = -3467.4078 (not concave)
Iteration 58: log likelihood = -3467.4078 (not concave)
Iteration 59: log likelihood = -3467.4078 (not concave)
Iteration 60: log likelihood = -3467.4078 (not concave)
Iteration 61: log likelihood = -3467.4078 (not concave)
Iteration 62: log likelihood = -3467.4078 (not concave)
Iteration 63: log likelihood = -3467.4078 (not concave)
Iteration 64: log likelihood = -3467.4078 (not concave)
Iteration 65: log likelihood = -3467.4078 (not concave)
Iteration 66: log likelihood = -3467.4078 (not concave)
Iteration 67: log likelihood = -3467.4078 (not concave)
Iteration 68: log likelihood = -3467.4078 (not concave)
Iteration 69: log likelihood = -3467.4078 (not concave)
Iteration 70: log likelihood = -3467.4078 (not concave)
Iteration 71: log likelihood = -3467.4078 (not concave)
Iteration 72: log likelihood = -3467.4078 (not concave)
Iteration 73: log likelihood = -3467.4078 (not concave)
Iteration 74: log likelihood = -3467.4078 (not concave)
Iteration 75: log likelihood = -3467.4078 (not concave)
Iteration 76: log likelihood = -3467.4078 (not concave)
Iteration 77: log likelihood = -3467.4078 (not concave)
Iteration 78: log likelihood = -3467.4078 (not concave)
Iteration 79: log likelihood = -3467.4078 (not concave)
Iteration 80: log likelihood = -3467.4078 (not concave)
Iteration 81: log likelihood = -3467.4078 (not concave)
Iteration 82: log likelihood = -3467.4078 (not concave)
Iteration 83: log likelihood = -3467.4078 (not concave)
Iteration 84: log likelihood = -3467.4078 (not concave)
Iteration 85: log likelihood = -3467.4078 (not concave)
Iteration 86: log likelihood = -3467.4078 (not concave)
Iteration 87: log likelihood = -3467.4078 (not concave)
Iteration 88: log likelihood = -3467.4078 (not concave)
Iteration 89: log likelihood = -3467.4078 (not concave)
Iteration 90: log likelihood = -3467.4078 (not concave)
Iteration 91: log likelihood = -3467.4078 (not concave)
Iteration 92: log likelihood = -3467.4078 (not concave)
Iteration 93: log likelihood = -3467.4078 (not concave)
Iteration 94: log likelihood = -3467.4078 (not concave)
Iteration 95: log likelihood = -3467.4078 (not concave)
Iteration 96: log likelihood = -3467.4078 (not concave)
Iteration 97: log likelihood = -3467.4078 (not concave)
Iteration 98: log likelihood = -3467.4078 (not concave)
Iteration 99: log likelihood = -3467.4078 (not concave)
Iteration 100: log likelihood = -3467.4078 (not concave)
Iteration 101: log likelihood = -3467.4078 (not concave)
Iteration 102: log likelihood = -3467.4078 (not concave)
Iteration 103: log likelihood = -3467.4078 (not concave)
Iteration 104: log likelihood = -3467.4078 (not concave)
Iteration 105: log likelihood = -3467.4078 (not concave)
Iteration 106: log likelihood = -3467.4078 (not concave)
Iteration 107: log likelihood = -3467.4078 (not concave)
Iteration 108: log likelihood = -3467.4078 (not concave)
Iteration 109: log likelihood = -3467.4078 (not concave)
Iteration 110: log likelihood = -3467.4078 (not concave)
Iteration 111: log likelihood = -3467.4078 (not concave)
Iteration 112: log likelihood = -3467.4078 (not concave)
Iteration 113: log likelihood = -3467.4078 (not concave)
Iteration 114: log likelihood = -3467.4078 (not concave)
Iteration 115: log likelihood = -3467.4078 (not concave)
Iteration 116: log likelihood = -3467.4078 (not concave)
Iteration 117: log likelihood = -3467.4078 (not concave)
Iteration 118: log likelihood = -3467.4078 (not concave)

etc ....

Any suggestion please?