diff --git a/ftml.lua b/ftml.lua new file mode 100644 index 0000000..0ffb2ce --- /dev/null +++ b/ftml.lua @@ -0,0 +1,69 @@ +--[[ An implementation of FTML http://www.cse.ust.hk/~szhengac/papers/icml17.pdf + +ARGS: +- 'opfunc' : a function that takes a single input (X), the point + of a evaluation, and returns f(X) and df/dX +- 'x' : the initial point +- 'config` : a table with configuration parameters for the optimizer +- 'config.learningRate' : learning rate +- `config.learningRateDecay` : learning rate decay +- 'config.beta1' : first moment coefficient +- 'config.beta2' : second moment coefficient +- 'config.epsilon' : for numerical stability +- 'config.weightDecay' : weight decay +- 'state' : a table describing the state of the optimizer; after each + call the state is modified +RETURN: +- `x` : the new x vector +- `f(x)` : the function, evaluated before the update +]] + +function optim.ftml(opfunc, x, config, state) + -- (0) get/update state + local config = config or {} + local state = state or config + local lr = config.learningRate or 0.0025 + local lrd = config.learningRateDecay or 0 + local epsilon = config.epsilon or 1e-8 + local beta1 = config.beta1 or 0.6 + local beta2 = config.beta2 or 0.999 + local wd = config.weightDecay or 0 + + -- (1) evaluate f(x) and df/dx + local fx, dfdx = opfunc(x) + + -- (2) weight decay + if wd ~= 0 then + dfdx:add(wd, x) + end + + -- Initialization + state.t = state.t or 0 + -- z in the paper + state.z = state.z or x.new(dfdx:size()):zero() + -- Exponential moving average of squared gradient values + state.v = state.v or x.new(dfdx:size()):zero() + -- Temp tensor + state.denom = state.denom or x.new(dfdx:size()):zero() + -- Last temp tensor + state.denom_old = state.denom_old or x.new(dfdx:size()):zero() + + -- (3) learning rate decay (annealing) + local clr = lr / (1 + state.t*lrd) + + state.t = state.t + 1 + local biasCorrection1 = 1 - beta1^state.t + local biasCorrection2 = 1 - beta2^state.t + + -- Decay the running average coefficient + state.v:mul(beta2):addcmul(1-beta2, dfdx, dfdx) + state.denom:copy(state.v):sqrt():mul(biasCorrection1/(math.sqrt(biasCorrection2)*clr)):add((biasCorrection1*epsilon)/clr) + state.z:mul(beta1):add(1-beta1, dfdx):addcmul(1, x, state.denom_old:mul(beta1):csub(state.denom)) + state.denom_old:copy(state.denom) + + -- (4) update x + x:cdiv(state.z, state.denom:mul(-1)) + + -- return x*, f(x) before optimization + return x, {fx} +end \ No newline at end of file