Document return types of custom c functions

[CGMossa]

In order to circumvent #291, I decided to try to make a c-function, that takes a rectangular matrix, and performs some calculation on an array.
But there must be a LHS to all lines;
And thus I need a return type that means "2-d array" or even "1-D array".

Is it possible to know how this could look like?
I've tried double* and double**, but that gave complaints.

[CGMossa]

I'm reopening this because I have a hard time figuring out what is allowed and not.
In C, we cannot return arrays.
An idea would be to use void c_function(size_t len, const double* input, double* output), but that doesn't work because odin expects a LHS to every line.
I want to do an operation on a long array $M × 3$, and then use that to fill out vectors.
But to do so, I'm expected to use i for the output vector $N ×1$. But then how can I perform the calculation on the former, store it, and then use its content on filling out N×1. if I just have a dummy <- c_function(...) it doesn't appear in the odin.c file generated, as in doesn't appear when things are happening.

[CGMossa]

It is as if I'm unable to pass a double** arr to a custom c-function..