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Date: Tue, 18 Sep 2012 03:18:14 -0700 (PDT)
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Subject: Re: problem with Real_Matrix*Real_Matrix
From: Anatoly Chernyshev <achernyshev@gmail.com>
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Date: 2012-09-18T03:18:14-07:00
List-Id: <comp.lang.ada>

Got the same mistake on Win7/GNAT 2012. As I'm doing matrix calculations too, I had to investigate, and here's the culprit from s-gearop.adb:
---------------------------------------------------------------
   function Vector_Matrix_Product
     (Left  : Left_Vector;
      Right : Matrix) return Result_Vector
   is
   begin
      return R : Result_Vector (Right'Range (2)) do
         if Left'Length /= Right'Length (2) then
            raise Constraint_Error with
              "incompatible dimensions in vector-matrix multiplication";
         end if;

         for J in Right'Range (2) loop
            declare
               S : Result_Scalar := Zero;

            begin
               for K in Right'Range (1) loop
                  S := S + Left (J - Right'First (1)
                                   + Left'First) * Right (K, J);
               end loop;

               R (J) := S;
            end;
         end loop;
      end return;
   end Vector_Matrix_Product;
---------------------------------------------------------------
S := S + Left (J - Right'First (1) + Left'First) * Right (K, J); - in this fragment Left is kept constant within the K-cycle. Replacing Left'First with K would correct the problem. 

I believe, it was straightened for some reason for the Mac distribution; would be interesting to compare.