[Insight-users] Another question about the optimizer.

[Raghavendra Chandrashekara]

Dear All,

I've written a simple program which registers a sphere to a cube using 
the itk::MeanSquaresImageToImageMetric, 
itk::RegularGradientDescentOptimizer, and the 
itk::BSplineDeformableTransform classes. At the end of each iteration 
I've printed out the value of the metric and these are the values I get:

Iteration 0 = 12499.2
Iteration 1 = 10638.3
Iteration 2 = 9153.67
Iteration 3 = 7949.65
Iteration 4 = 7119.97
Iteration 5 = 6549.05
Iteration 6 = 6009.38
Iteration 7 = 5607.8
Iteration 8 = 5330.65
Iteration 9 = 4985.47
Iteration 10 = 4669.74
Iteration 11 = 4395.71
Iteration 12 = 4067.56
Iteration 13 = 3753.94
Iteration 14 = 3608.51
Iteration 15 = 3327.5
Iteration 16 = 3067.84
Iteration 17 = 2744.56
Iteration 18 = 2453.56
Iteration 19 = 2269.56
Iteration 20 = 2045.05
Iteration 21 = 1795.79
Iteration 22 = 1685.94
Iteration 23 = 1544.54
Iteration 24 = 1510.56
Iteration 25 = 1377.79
Iteration 26 = 1465.86
Iteration 27 = 1566.17
Iteration 28 = 1198.16
Iteration 29 = 1420.57
Iteration 30 = 1043.68
Iteration 31 = 1392.55
Iteration 32 = 1011.74
Iteration 33 = 1285.96
Iteration 34 = 897.961
Iteration 35 = 1304.93
Iteration 36 = 1022.35
Iteration 37 = 946.78
Iteration 38 = 918.44
Iteration 39 = 950.961
Iteration 40 = 915.875
Iteration 41 = 964.306
Iteration 42 = 807.392
Iteration 43 = 951.763
Iteration 44 = 731.597
Iteration 45 = 824.336
Iteration 46 = 828.187
Iteration 47 = 792.121
Iteration 48 = 781.585
Iteration 49 = 808.127

Everything seems okay until iteration 26, when the metric value 
increases. Shouldn't the optimizer stop the registration at this point 
since it can't improve the metric anymore?

Thanks,

Raghavendra