Is it possible to optimize a table of modules together?

[squidszyd]

I'm currently working on a project where there are two modules that need to be optimized. And these two modules are somewhat relative to each other. I'm wondering if it is possible to optimize them together using optim? For example, could I write a feval function whose input is a table of parameters: { paramFromModule1, paramFromModule2 } and returns a table of grads: { gradsFromModule1, gradsFromModule2 }?

[taineleau-zz]

Yes. I guess what you need is the following. x is a table of parameters.

local function sgd_custom(opfunc, x, config, state)
   -- (0) get/update state
   local config = config or {}
   local state = state or config
   local lr = config.learningRate or 1e-3
   local lrd = config.learningRateDecay or 0
   local wd = config.weightDecay or 0
   local mom = config.momentum or 0
   local damp = config.dampening or mom
   local nesterov = config.nesterov or false
   local lrs = config.learningRates
   local wds = config.weightDecays
   state.evalCounter = state.evalCounter or 0
   local nevals = state.evalCounter
   assert(not nesterov or (mom > 0 and damp == 0), "Nesterov momentum requires a momentum and zero dampening")

   -- (1) evaluate f(x) and df/dx
   local fx,dfdx = opfunc(x)

   -- (2) weight decay with single or individual parameters
   if wd ~= 0 then
      for i=1, #dfdx do
         dfdx[i]:add(wd, x[i])
      end
   elseif wds then
      if not state.decayParameters then
         state.decayParameters = torch.Tensor():typeAs(x):resizeAs(dfdx)
      end
      state.decayParameters:copy(wds):cmul(x)
      dfdx:add(state.decayParameters)
   end

   -- (3) apply momentum
   if mom ~= 0 then
      if not state.dfdx then
         state.dfdx = {}
         for i=1, #dfdx do
            state.dfdx[i] = torch.Tensor():typeAs(dfdx[i]):resizeAs(dfdx[i]):copy(dfdx[i])
         end
      else
         for i=1, #dfdx do
            state.dfdx[i]:mul(mom):add(1-damp, dfdx[i])
         end
      end
      if nesterov then
         for i=1,#dfdx do
            dfdx[i]:add(mom, state.dfdx[i])
         end
      else
         for i=1, #dfdx do
            dfdx[i] = state.dfdx[i]
         end
      end
   end

   -- (4) learning rate decay (annealing)
   local clr = lr / (1 + nevals*lrd)

   -- (5) parameter update with single or individual learning rates
   if lrs then
      if not state.deltaParameters then
         state.deltaParameters = torch.Tensor():typeAs(x):resizeAs(dfdx)
      end
      state.deltaParameters:copy(lrs):cmul(dfdx)
      x:add(-clr, state.deltaParameters)
   else
      for i=1, #x do
         x[i]:add(-clr, dfdx[i])
      end
   end
   -- (6) update evaluation counter
   state.evalCounter = state.evalCounter + 1

   -- return x*, f(x) before optimization
   return x,{fx}
end

Or you may just put these models under a same custom nn.Container.

[squidszyd]

@taineleau Thank you! I've also found that combine_all_parameters could solve my issue.