Symbolic programming in MXNet

Let us do some symbolic declaration:

> a <- mx.symbol.Variable("a")
> a
C++ object <0x11dea3e00> of class 'MXSymbol' <0x10c0a79b0>
> b <- mx.symbol.Variable("b")
> b
C++ object <0x10fecf330> of class 'MXSymbol' <0x10c0a79b0>
> c <- a + b
> c
C++ object <0x10f91bba0> of class 'MXSymbol' <0x10c0a79b0>
>

As you can see, they are MXSymbol objects.

We need an executor to supply data to it and to get the results:

> arg_lst <- list(symbol = c, ctx = mx.ctx.default(), a = dim(ones.matrix),
+                 b= dim(ones.matrix), grad.req="null")
> pexec <- do.call(mx.simple.bind, arg_lst)
> pexec
C++ object <0x11d852c40> of class 'MXExecutor' <0x101be9c30>
> input_list <-  list(a = ones.matrix,b = ones.matrix)
> mx.exec.update.arg.arrays(pexec, input_list)
> mx.exec.forward(pexec)
> pexec$arg.arrays
$a
     [,1] [,2] [,3]
[1,]    1    1    1
[2,]    1    1    1
[3...