RE: [vhdl-200x] Please Review Matrix Math Package

On Friday, June 27, 2014 10:39 AM David Bishop wrote:
>On 06/26/2014 10:09 PM, tgingold@free.fr wrote:
>> I am slightly confused by the representation.  In the ug:
>>
>> As a concession to C, all matrices are assumed to be in column, row format, and starting at index 0. Thus for the matrix:
>> Z := ((1.0, 2.0, 3.0),
>>        (4.0, 5.0, 6.0),
>>        (7.0, 8.0, 9.0));
>> Z (0,2) = 7.0
>>
>>
>> I suppose we all agree that Z should be:
>> [ 1 2 3
>>    4 5 6
>>    7 8 9 ]
>>
>> So the first dimension is the number of lines and the second dimension is the number of columns.
>> This is natural both from a point of view of the VHDL language and from classical math style.
>>
>> But in that case and following the above excerpt, Z (0, 2) is 3.0 !
>
>When I create a matrix, I do it as:
>   type real_matrix is array (NATURAL range <>, NATURAL range <>) of REAL;  -- real matrix Which follows from:
>   type real_vector is array (NATURAL range <>) of REAL; Which is part of VHDL-2008.
>
>So what you really have is array of arrays.   In order to load the 
>array, I have to do:
>
>Z := ((1.0, 2.0, 3.0),
>       (4.0, 5.0, 6.0),
>       (7.0, 8.0, 9.0));
>
>which reversed rows and columns as it loads.....

I strongly agree with Tristan that we want to keep the (row, column) index semantics.  I can imagine the reverse making the package too confusing to be useful to me.  (I would probably write an auxiliary package to somehow make the natural ordering convenient for me.)  I also agree with Tristan's assessment that both mathematics and VHDL syntax match this convention.  So in the array he defines, Z(0,2) is 3.0.  In fact, I tried it (code at the end of the email).  My simulator prints:

Element (0,2) is 3.000000e+00

So, David, I'm confused by your conclusion that the aggregate "[reverses] rows and columns as it loads."  

>> BTW, I am not sure that starting at index "0" is the best choice.  
>> This is neither the matlab conversion (which is heavily used) nor the math choice.

I still like the 0-based index.  Since this is VHDL, you can define your objects 1-based if you like.  Matlab's 1-based types make my life harder.  I write my VHDL and math to used 0-based indices.

- Ryan

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