Fig. 5.

Decay of the criterion (10) as a function of the number of CG iterations. The dotted lines mark the locations of the level-set update, where the support of the activations are changed. Each support update will add or delete new voxels to the current estimate of the support. The newly added voxels are initialized by zeros to start the CG iteration. This results in a slight increase in the value of the criterion [mainly due to a high value of the third term in Eq. (10)] after some of the support updates (at the steps where new voxels are added). Note that in these steps, the criterion decays to a value smaller than the one before the support update in a few iterations. Both the CG and the level-set iterations are terminated when the relative decrease in the criterion falls below a specified threshold.