Normalize a histogram modification

What do I need to put in to normalize the distribution?

function y = mkhist(lambda, n_mea, n_smpls_per_mea)
   %program to fix up histogram (normalization, etc) and 
   %prepare plots with both histogram and the analytical PDF
   %called AFTER a call to 'run'

    global xacc  hist  bin_range  bin_size  n_bins  midpt x exact_pdf
      % normalize histogram (histnorm_inv is INVERSE of normalization):
    histnorm_inv = 1.
      %           ^^^^^^^^ <-- MODIFY -- fill in correct form 
    hist = hist.*histnorm_inv
      % Calculate the exact distribution for comparison
    x=0:bin_size:bin_range+bin_size
    exact_pdf = exp(-x/lambda)/lambda
    end

[Jan]

This is the 3rd thread concerning the same problem. This starts to be confusing. Usually the readers in the forum tends to ignore confusing threads, so better concentrate on one thread and answer the question for clarifications. This is easier for the readers and increases your chance to get an answer.