## MAfSyBilin

#### Routine

double MAfSyBilin (const float *A[], const float x[], const float y[], int N)

#### Purpose

Calculate a bilinear form for a symmetric matrix

#### Description

This routine calculates the bilinear form s = x'A y for vectors x and y, and symmetric matrix A,

          N-1 N-1
      s = SUM SUM x(i) A(i,j) y(j) .
          i=0 j=0

The symmetry of A is used to reduce the number of computations. The result is accumulated as a double value and returned as a double value.

#### Parameters

<- double MAfSyBilin
  Returned value
-> const float *A[]
  A is an array of pointers to the rows of an N by N matrix. The matrix is assumed to be symmetric. Only the lower triangular portion of the matrix is accessed. Note that with ANSI C, if the actual parameter is not declared to have the const attribute, an explicit cast to (const float **) is required.
-> const float x[]
  Input vector (N elements)
-> const float y[]
  Input vector (N elements)
-> int N
  Number of of elements in x and y and the size of A

#### Author / revision

P. Kabal / Revision 1.5 2003/05/09

#### See Also

MAfSyQuad, MAfTpQuad

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