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From: =?UTF-8?Q?Nicholas_Collin_Paul_de_Glouce=C5=BFter?=
 <Colin_Paul_Gloster@ACM.org>
Newsgroups: comp.lang.ada
Subject: Re: Incorrect error?
Date: Mon, 18 Jul 2011 10:39:55 +0000
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Date: 2011-07-18T10:39:55+00:00
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L. Dries <bertus.dries@Planet.NL> sent on July 18th, 2011:
|--------------------------------------------------------------------------------|
|"I'm using Ada.Numerics.Generic_Real_Arrays. While Compiling I got the following|
|error message:                                                                  |
|                                                                                |
|65:21     expected type "Ada.Numerics.Generic_Real_Arrays.Real_Vector" from     |
|instance at line 6                                                              |
|65:21     found type "Ada.Numerics.Generic_Real_Arrays.Real_Matrix" from        |
|instance at line 6                                                              |
|                                                                                |
|As can be seen Cross, a and b declared as Real_Vector .                         |
|What do I do wrong?                                                             |
|                                                                                |
|L. Dries                                                                        |
|                                                                                |
|[..]                                                                            |
|  a      : Real_Vector(0 .. 2);                                                 |
|  b      : Real_Vector(0 .. 2);                                                 |
|[..]                                                                            |
|  cross  : Real_Vector(0 .. 2);                                                 |
|[..]                                                                            |
|     a := X1 - X0; -- VecSub( a, X1, X0 );                                      |
|     b := X2 - X0; -- VecSub( b, X2, X0 );                                      |
|    Cross := a * b; -- VecCross( a, b, Cross ); <---------------- line 65 the   |
|cursor is standing just before *                                                |
|[..]"                                                                           |
|--------------------------------------------------------------------------------|


The product of a 3x1 vector and a 1x3 vector is a 3x3 matrix.
The product of a 3x1 vector and a 3x1 vector can not exist.
You are trying to assign a 2d matrix (that is a * b) to a variable
declared to be a 1d vector.