MATH-LINALG(2)                                     MATH-LINALG(2)

     NAME
          Math: dot, norm1, norm2, iamax, gemm, sort - linear algebra
          primitives

     SYNOPSIS
          include   "math.m";
          math := load Math Math->PATH;

          dot: fn(x, y: array of real): real;
          norm1, norm2: fn(x: array of real): real;
          iamax: fn(x: array of real): int;
          gemm: fn(transa, transb: int,  # upper case N or T
                    m, n, k: int, alpha: real,
                    a: array of real, lda: int,
                    b: array of real, ldb: int, beta: real,
                    c: array of real, ldc: int);

          sort: fn(x: array of real, p: array of int);

     DESCRIPTION
          These routines implement the basic functions of linear
          algebra.  The standard vector inner product and norms are
          defined as follows:

               dot(x , y) = sum(x[i]*y[i])

               norm1(x) = sum(fabs(x[i ]))

               norm2(x) = sqrt(dot(x , x))

          For the infinity norm, the function iamax(x) computes an
          integer i such that fabs(x[i]) is maximal.  These are all
          standard BLAS (basic linear algebra subroutines) except that
          in Inferno they apply only to contiguous (unit stride) vec-
          tors.

          We assume the convention that matrices are represented as
          singly-subscripted arrays with Fortran storage order.  So
          for an m by n matrix A we use loops with 0_<i<m and 0_<j<n and
          access A[i+m*j].

          Rather than provide the huge number of entry points in BLAS2
          and BLAS3, Inferno provides the matrix multiply primitive,
          gemm, defined by

              A = A*A'*B' + B*C

          where the apostrophes indicate an optional transposition.
          As shown by the work of Kagstrom, Ling, and Van Loan, the
          other BLAS functionality can be built efficiently on top of

     Page 1                       Plan 9            (printed 12/22/24)

     MATH-LINALG(2)                                     MATH-LINALG(2)

          gemm.

          Matrix a' is m by k, matrix b' is k by n, and matrix c is m
          by n. Here a' means a (a') if transa is the constant 'N'
          ('T'), and similarly for b'. The sizes m, n, and k denote
          the `active' part of the matrix.  The parameters lda, ldb,
          and ldc denote the `leading dimension' or size for purposes
          of indexing.  So to loop over c use loops with 0_<i<m and
          0_<j<n and access a[i+ldc*j].

          The sorting function sort(x,p) updates a 0-origin permuta-
          tion p so that x[p[i]] _< x[p[i+1]], leaving x unchanged.

     SOURCE
          /libinterp/math.c

     SEE ALSO
          math-intro(2)

     Page 2                       Plan 9            (printed 12/22/24)