distance metric Subscripted assignment error

Hi

My test feature vector is 'testpg' and trained feature vector is 'trainpg' and both are of dimension 2000*1 .I am aiming to find the distance between the two histogram feature vectors and hence i do

distance =  norm(trainpg-testpg)

Next I compare it to a scalar threshold value to check whether it satisfies my condition , The above code works well as i get a scalar value of this distance ie : for eg distance = 5.4 which is a scalar

But when I change code to use any other histogram based distance metric it doesn't work

i used the pdist2 function from http://www.mathworks.com/matlabcentral/fileexchange/29004-feature-points-in-image--keypoint-extraction/content/FPS_in_image/FPS%20in%20image/Help%20Functions/SearchingMatches/pdist2.m

The new code I used is

    distance  = pdist2(trainpg,testpg, 'chisq')
     d = size(distance)

Here I am getting subscripted assignment dimension mismatch error as the dimensions of my distance are now 2000*2000 instead of 1*1

How could I get scalar value for the distances?