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The basic least-squares equations are often called
the ``**normal**" equations.
The word ``normal" means perpendicular.
We can rewrite equation
(16)
to emphasize the perpendicularity.
Bring both terms to the left,
and recall the definition of the residual from equation (2):

| |
(23) |

| (24) |

Equation (24) says that the **residual** vector is perpendicular to
each row in the matrix.
These rows are the **fitting function**s.
Therefore, the residual, after it has been minimized,
is perpendicular to the fitting functions.

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** Up:** MULTIVARIATE LEAST SQUARES
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Stanford Exploration Project

10/21/1998