sci_files How to write conversion functions

## Description

To convert calls to Matlab functions, `mfile2sci` uses a function called `sci_<Matlab_function_name>`. All these functions are defined in `sci_files` in directory SCI/modules/m2sci/macros/sci_files/. The set of `sci_files` given in Scilab distribution does not allow to convert calls to all Matlab functions yet. However, a Scilab user can add `sci_files` (for Matlab functions or for user defined functions) to Scilab using the following tips.

In M2SCI, a function call is considered as a "tree" (it is also the case for the instructions of the file to convert), represented in Scilab by a `tlist` with following fields:

- name

    Matlab function name

  lhsnb

    number of Matlab function output parameters

  lhs

    list of Matlab function output parameters

  rhs

    list of Matlab function input parameters

A `sci_function` has one input called `tree` which is also the output of the function. A `sci_function` has to convert this incoming "tree" so that it is compatible with Scilab by changing name, lhsnb, lhs and/or rhs. The other task that has to be done by this function is inference. Incoming tree contains inference data in its lhs that have to be updated with what can be infered for the outputs of this function.

Some useful functions have been written to help to create M2SCI tlists while writing this conversion function:

- Funcall

    create a tree representing a function call

  Operation

    create a tree representing an operation

  Variable

    create a tree representing a variable

  Cste

    create a tree representing a constant value

  Infer

    create a tree representing inference data

  Type

    create a tree representing type for inference

  Equal

    create a tree representing an instruction

Some other functions have been designed to get properties of operands/inputs. Considering A is tlist used in macro tree, you can use the following functions:

Function | returns `%T` if...
`is_empty(A)` | all dimensions of A are 0
`not_empty(A)` | all dimensions of A are known and at least one dimension of A is not 0
`is_a_scalar(A)` | all dimensions of A are 1
`not_a_scalar(A)` | all dimensions of A are known and at least one dimension of A is not 1
`is_a_vector(A)` | all dimensions of A are known and all dimensions of A but one are equal to 1
`not_a_vector(A)` | all dimensions of A are known and at least two dimensions of A are greater than one
`is_real(A)` | A is real
`is_complex(A)` | A is complex
`isdefinedvar(A)` | A is a variable already created in M-file currently converted
`allunknown(A)` | all dimensions of A are unknown

Some other functions have been written for specific needs while writing conversion files:

- first_non_singleton

    is an equivalent to firstnonsingleton for an M2SCI tlist. Syntax: `dim = first_non_singleton(A)`

  gettempvar

    generates a temporary variable having a name which does not already exist. Syntax:`v = gettempvar()`

  insert

    allows to insert instructions. Syntax:`m2sci_insert(Equal(...),opt)` with `opt~=1` to insert before current instruction and `opt=1` to insert after it.

  getoperands

    can be used to get each operand as a variable. Syntax: `[A,B] = getoperands(operation_tlist)`

  getrhs

    can be used to get each parameter as a variable. Syntax: `[A,...] = getrhs(funcall_tlist)`

  convert2double

    change type of input when this type is not implemented for a particular function is Scilab. Syntax:`A = convert2double(A)`

To have more information about how to write such files, refer to directory SCI/modules/m2sci/macros/sci_files/ which gives many examples from very simple ones (e.g. sci_abs.sci) to very complex ones (e.g. sci_zeros.sci).

## See also

- m2scideclare
- Funcall
- Operation
- Variable
- Cste
- Infer
- Type
- Equal