Need help with C Code Generator

Question

I'm trying to use the Mathematica C Code Generator package to generate code that is to be included in a web application by a developer. I don't know any C, and this seems to be the only way to integrate my model with the web-app. I am having a lot of difficulties getting off the ground.

A persistent error seems to be that my iteration indices are not recognised as integers. Here's an example:

Needs["CCodeGenerator`"]
funct = Compile[{{M, _Real, 2}, {l, _Integer}},
  Module[{matrix = M, lag = l },
   columns = Length[Transpose[matrix]];
    Flatten[ 
      Join[ {{{Table[1, {columns - lag + 1}]}}, 
      Table[matrix[[;; , lag - i + 1 ;; columns - i + 1]] , {i, 1, lag}]} ] , 2]
    ], {{i, _Integer}}
]

This produces the following error:

Compile::cpintlt: "1;;All at position 2 of matrix[[1;;All,lag-i+1;;columns+i+1]] should be either a nonzero integer or a vector of nonzero integers; evaluation will use the uncompiled function."

Finally when I export the C code, I get errors like

CCodeGenerate::wmreq: "The expression Function[{M,l,iCompile$18},Block[{i=iCompile$18},{All,i}]] requires Mathematica to be evaluated. The function will be generated but can be expected to fail with a nonzero error code when executed. "

Any help would be greatly appreciated.

Answer 1

It looks like Compile doesn't handle 1;;All in Span, so why not just use explicit total number of rows?

Compile[{{matrix, _Real, 2}, {lag, _Integer}},
    Module[{rows, columns},
        {rows, columns} = Dimensions[matrix];
        Join[
            {Table[1., {columns - lag + 1}]},
            Flatten[
                Table[
                    matrix[[1 ;; rows, lag - i + 1 ;; columns - i + 1]],
                    {i, 1, lag}],
                1]]]] //
   CCodeGenerate[ #, "fun", "generatedfunc.c"] &

Also please note you leave the columns as an external variable, which will cause the MainEvaluate call.

Edit:

However, as pointed out by xzczd, Compile does handle All correctly as matrix[[All, lag - i + 1 ;; columns - i + 1]].