It is important to know if vector v2 is sorted. If it is, then use histc, which will quickly give you the index of the elements just under each element of v1.
Then you check to see if the element above the ones you just found is closer.
Finally, if the vector v2 is NOT sorted, then it is still simple. Just do s sort on v2, to create a vector v3. Keep the tags from that sort. Now, use the scheme I mentioned above to find the closest point in v3. Use the tags from the sort to back out the original index of those elements. If all you needed is the actual closest value, then there is no need to do this last step.
Note that ALL of the above ops are vectorizable. No explicit loops are necessary to do anything I suggested above.
