add normalize_sums utility function

util.lua

@@ -1,5 +1,6 @@
 -- TODO: reorganize function order.
 
+local abs = math.abs
 local assert = assert
 local exp = math.exp
 local ipairs = ipairs
@@ -93,6 +94,17 @@ local function normalize_wrt(x, s, out)
     return out
 end
 
+local function normalize_sums(x, out)
+    out = out or x
+    local sum = 0
+    for i, v in ipairs(x) do sum = sum + v end
+    for i, v in ipairs(x) do out[i] = v - sum / #x end
+    local abssum = 0
+    for i, v in ipairs(out) do abssum = abssum + abs(v) end
+    for i, v in ipairs(out) do out[i] = v / abssum end
+    return out
+end
+
 local function fitness_shaping(rewards)
     -- lifted from: https://github.com/atgambardella/pytorch-es/blob/master/train.py
     local decreasing = nn.copy(rewards)
@@ -207,6 +219,7 @@ return {
     calc_mean_dev=calc_mean_dev,
     normalize=normalize,
     normalize_wrt=normalize_wrt,
+    normalize_sums=normalize_sums,
     fitness_shaping=fitness_shaping,
     unperturbed_rank=unperturbed_rank,
     copy=copy,